release: cut v2.4.0 — per-event colors

Optional per-event color in the event form. The read/render path already
resolved EVENT_COLOR with a calendar fallback; this adds the write side and
the picker.

- Palette-backed calendars (Google, some CalDAV) pick from the account's
  Colors (TYPE_EVENT) and write EVENT_COLOR_KEY, so the color round-trips
  through sync; local calendars write a raw EVENT_COLOR from the shared
  CALENDAR_COLOR_PALETTE. Never writes a raw color to a palette calendar.
- Swatch row + palette extracted to ui/common/ColorSwatchRow.kt (shared with
  the calendar editor). Switching calendars resets the choice (keys are
  account-scoped); a "Reset" action returns to the calendar color.
- New "Allow colors on unsupported calendars" setting (off by default)
  extends the raw path to no-palette synced calendars, with an honest
  "may not survive sync" warning on the picker and in Settings.
- Color flows through insert / dirty-checked update / occurrence-exception;
  mapper, form, and repository tests added.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt

@@ -14,6 +14,7 @@ import android.util.Log
 import dagger.hilt.android.qualifiers.ApplicationContext
 import de.jeanlucmakiola.calendula.domain.Attendee
 import de.jeanlucmakiola.calendula.domain.CalendarSource
+import de.jeanlucmakiola.calendula.domain.EventColorOption
 import de.jeanlucmakiola.calendula.domain.EventDetail
 import de.jeanlucmakiola.calendula.domain.EventForm
 import de.jeanlucmakiola.calendula.domain.EventInstance
@@ -37,6 +38,15 @@ interface CalendarDataSource {
     fun instances(beginMillis: Long, endMillis: Long): List<EventInstance>
     fun eventDetail(eventId: Long): EventDetail?
 
+    /**
+     * The event-colour palette the calendar's account publishes
+     * (`CalendarContract.Colors`, `TYPE_EVENT`), sorted by key. Empty when the
+     * account exposes no palette (most local calendars, some CalDAV) — the
+     * signal that a custom colour can only be written as a raw `EVENT_COLOR`,
+     * which a synced calendar may drop on its next sync.
+     */
+    fun eventColorPalette(calendarId: Long): List<EventColorOption>
+
     /**
      * Create a new device-only (`ACCOUNT_TYPE_LOCAL`) calendar the app owns;
      * returns its `Calendars._ID`. Inserted through the sync-adapter URI so the
@@ -215,6 +225,46 @@ class AndroidCalendarDataSource @Inject constructor(
         }
     }
 
+    override fun eventColorPalette(calendarId: Long): List<EventColorOption> {
+        val account = calendarAccount(calendarId) ?: return emptyList()
+        return resolver.query(
+            CalendarContract.Colors.CONTENT_URI,
+            arrayOf(CalendarContract.Colors.COLOR_KEY, CalendarContract.Colors.COLOR),
+            CalendarContract.Colors.ACCOUNT_NAME + " = ? AND " +
+                CalendarContract.Colors.ACCOUNT_TYPE + " = ? AND " +
+                CalendarContract.Colors.COLOR_TYPE + " = ?",
+            arrayOf(
+                account.name,
+                account.type,
+                CalendarContract.Colors.TYPE_EVENT.toString(),
+            ),
+            null,
+        )?.use { c ->
+            c.mapAll { EventColorOption(key = it.getString(0).orEmpty(), argb = it.getInt(1)) }
+        }
+            ?.filter { it.key.isNotEmpty() }
+            ?.sortedBy { it.key }
+            ?: emptyList()
+    }
+
+    /** The account a calendar belongs to, for scoping a `Colors` lookup. */
+    private fun calendarAccount(calendarId: Long): CalendarAccount? = resolver.query(
+        ContentUris.withAppendedId(CalendarContract.Calendars.CONTENT_URI, calendarId),
+        arrayOf(
+            CalendarContract.Calendars.ACCOUNT_NAME,
+            CalendarContract.Calendars.ACCOUNT_TYPE,
+        ),
+        null, null, null,
+    )?.use { c ->
+        if (c.moveToFirst()) {
+            CalendarAccount(name = c.getString(0).orEmpty(), type = c.getString(1).orEmpty())
+        } else {
+            null
+        }
+    }
+
+    private data class CalendarAccount(val name: String, val type: String)
+
     override fun insertEvent(form: EventForm): Long {
         val times = form.toWriteTimes(ZoneId.systemDefault())
         val values = ContentValues().apply {
@@ -240,6 +290,13 @@ class AndroidCalendarDataSource @Inject constructor(
                 ?.let { put(CalendarContract.Events.EVENT_LOCATION, it) }
             form.description.trim().takeIf { it.isNotEmpty() }
                 ?.let { put(CalendarContract.Events.DESCRIPTION, it) }
+            // A null colour just leaves both columns unset (the event inherits
+            // its calendar's colour), so only the key/raw cases are written.
+            when {
+                form.colorKey != null ->
+                    put(CalendarContract.Events.EVENT_COLOR_KEY, form.colorKey)
+                form.color != null -> put(CalendarContract.Events.EVENT_COLOR, form.color)
+            }
         }
         val uri = resolver.insert(CalendarContract.Events.CONTENT_URI, values)
             ?: throw WriteFailedException("insert event into calendar id=${form.calendarId}")

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarRepository.kt

@@ -1,6 +1,7 @@
 package de.jeanlucmakiola.calendula.data.calendar
 
 import de.jeanlucmakiola.calendula.domain.CalendarSource
+import de.jeanlucmakiola.calendula.domain.EventColorOption
 import de.jeanlucmakiola.calendula.domain.EventDetail
 import de.jeanlucmakiola.calendula.domain.EventForm
 import de.jeanlucmakiola.calendula.domain.EventInstance
@@ -12,6 +13,12 @@ interface CalendarRepository {
     fun instances(range: ClosedRange<Instant>): Flow<List<EventInstance>>
     suspend fun eventDetail(eventId: Long): EventDetail
 
+    /**
+     * The event-colour palette a calendar's account publishes; empty when it
+     * exposes none (see [CalendarDataSource.eventColorPalette]).
+     */
+    suspend fun eventColorPalette(calendarId: Long): List<EventColorOption>
+
     /** Create a device-only (LOCAL) calendar the app owns; returns its id. */
     suspend fun createLocalCalendar(displayName: String, color: Int, description: String?): Long
 

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarRepositoryImpl.kt

@@ -3,6 +3,7 @@ package de.jeanlucmakiola.calendula.data.calendar
 import de.jeanlucmakiola.calendula.data.di.IoDispatcher
 import de.jeanlucmakiola.calendula.data.prefs.CalendarPrefs
 import de.jeanlucmakiola.calendula.domain.CalendarSource
+import de.jeanlucmakiola.calendula.domain.EventColorOption
 import de.jeanlucmakiola.calendula.domain.EventDetail
 import de.jeanlucmakiola.calendula.domain.EventForm
 import de.jeanlucmakiola.calendula.domain.EventInstance
@@ -70,6 +71,9 @@ class CalendarRepositoryImpl @Inject constructor(
         dataSource.eventDetail(eventId) ?: throw NoSuchEventException(eventId)
     }
 
+    override suspend fun eventColorPalette(calendarId: Long): List<EventColorOption> =
+        withContext(io) { dataSource.eventColorPalette(calendarId) }
+
     override suspend fun createLocalCalendar(
         displayName: String,
         color: Int,

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapper.kt

@@ -46,11 +46,16 @@ internal fun ColumnReader.toEventDetailCore(
     // localized placeholder, and the edit form must prefill the true value.
     val title = getString(EventDetailProjection.IDX_TITLE).orEmpty()
 
-    val color = if (isNull(EventDetailProjection.IDX_EVENT_COLOR)) {
-        getInt(EventDetailProjection.IDX_CALENDAR_COLOR)
+    // The event's own colour (null = inherits the calendar's) is kept apart
+    // from the resolved display colour: the edit form needs to tell the two
+    // cases apart, while the instance carries the calendar fallback for display.
+    val eventColor = if (isNull(EventDetailProjection.IDX_EVENT_COLOR)) {
+        null
     } else {
         getInt(EventDetailProjection.IDX_EVENT_COLOR)
     }
+    val eventColorKey = getString(EventDetailProjection.IDX_EVENT_COLOR_KEY)
+    val color = eventColor ?: getInt(EventDetailProjection.IDX_CALENDAR_COLOR)
 
     val eventId = getLong(EventDetailProjection.IDX_EVENT_ID)
     val instance = EventInstance(
@@ -87,6 +92,8 @@ internal fun ColumnReader.toEventDetailCore(
         accessLevel = mapAccessLevel(getInt(EventDetailProjection.IDX_ACCESS_LEVEL)),
         eventTimezone = getString(EventDetailProjection.IDX_EVENT_TIMEZONE),
         selfStatus = mapAttendeeStatus(getInt(EventDetailProjection.IDX_SELF_ATTENDEE_STATUS)),
+        eventColor = eventColor,
+        eventColorKey = eventColorKey,
     )
 }
 

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventWriteMapper.kt

@@ -85,6 +85,9 @@ internal fun buildEventUpdateValues(
     if (updated.accessLevel != original.accessLevel) {
         put(CalendarContract.Events.ACCESS_LEVEL, updated.accessLevel.toProviderValue())
     }
+    if (updated.colorKey != original.colorKey || updated.color != original.color) {
+        putAll(eventColorColumns(updated.colorKey, updated.color))
+    }
 
     val timesChanged = updated.start != original.start ||
         updated.end != original.end ||
@@ -134,6 +137,28 @@ internal fun buildOccurrenceExceptionValues(
     put(CalendarContract.Events.ACCESS_LEVEL, form.accessLevel.toProviderValue())
     put(CalendarContract.Events.EVENT_LOCATION, form.location.trim().ifEmpty { null })
     put(CalendarContract.Events.DESCRIPTION, form.description.trim().ifEmpty { null })
+    putAll(eventColorColumns(form.colorKey, form.color))
+}
+
+/**
+ * The `EVENT_COLOR` / `EVENT_COLOR_KEY` columns for a colour selection. A
+ * [colorKey] writes the key alone (the provider derives `EVENT_COLOR` from the
+ * account's palette, so the colour round-trips through sync); a raw [color]
+ * writes `EVENT_COLOR` and clears any key; "no colour" clears both so the event
+ * falls back to its calendar's colour. The two are never written together —
+ * the provider rejects a raw colour on a calendar that publishes a palette,
+ * which is exactly why palette calendars only ever go through the key.
+ */
+internal fun eventColorColumns(colorKey: String?, color: Int?): Map<String, Any?> = when {
+    colorKey != null -> mapOf(CalendarContract.Events.EVENT_COLOR_KEY to colorKey)
+    color != null -> mapOf(
+        CalendarContract.Events.EVENT_COLOR_KEY to null,
+        CalendarContract.Events.EVENT_COLOR to color,
+    )
+    else -> mapOf(
+        CalendarContract.Events.EVENT_COLOR_KEY to null,
+        CalendarContract.Events.EVENT_COLOR to null,
+    )
 }
 
 /**

app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/Projections.kt

@@ -74,6 +74,7 @@ internal object EventDetailProjection {
         CalendarContract.Events.ACCESS_LEVEL,
         CalendarContract.Events.EVENT_TIMEZONE,
         CalendarContract.Events.SELF_ATTENDEE_STATUS,
+        CalendarContract.Events.EVENT_COLOR_KEY,
     )
 
     const val IDX_EVENT_ID = 0
@@ -93,6 +94,7 @@ internal object EventDetailProjection {
     const val IDX_ACCESS_LEVEL = 14
     const val IDX_EVENT_TIMEZONE = 15
     const val IDX_SELF_ATTENDEE_STATUS = 16
+    const val IDX_EVENT_COLOR_KEY = 17
 }
 
 internal object AttendeeProjection {

app/src/main/java/de/jeanlucmakiola/calendula/data/prefs/SettingsPrefs.kt

@@ -99,6 +99,22 @@ class SettingsPrefs @Inject constructor(
         store.edit { it[REMINDERS_ENABLED_KEY] = enabled }
     }
 
+    /**
+     * Whether to offer a custom event colour even on calendars that publish no
+     * colour palette (most local calendars handle it fine; synced calendars
+     * without a palette — some CalDAV — may drop or overwrite a raw colour on
+     * their next sync). Defaults to OFF: such calendars hide the colour picker
+     * until the user opts in, accepting the limitation. Local calendars and
+     * palette-backed calendars (Google, …) are unaffected by this flag.
+     */
+    val allowColorOnUnsupportedCalendars: Flow<Boolean> = store.data.map { prefs ->
+        prefs[ALLOW_COLOR_UNSUPPORTED_KEY] ?: false
+    }
+
+    suspend fun setAllowColorOnUnsupportedCalendars(enabled: Boolean) {
+        store.edit { it[ALLOW_COLOR_UNSUPPORTED_KEY] = enabled }
+    }
+
     /**
      * Whether the one-time reminder onboarding step (after the calendar
      * grant) has been shown — also true for users who tapped "not now".
@@ -125,6 +141,8 @@ class SettingsPrefs @Inject constructor(
         internal val FORM_FIELDS_KEY = stringPreferencesKey("event_form_default_fields")
         internal val REMINDERS_ENABLED_KEY = booleanPreferencesKey("reminders_enabled")
         internal val REMINDER_ONBOARDING_KEY = booleanPreferencesKey("reminder_onboarding_done")
+        internal val ALLOW_COLOR_UNSUPPORTED_KEY =
+            booleanPreferencesKey("allow_color_unsupported_calendars")
         internal val DEFAULT_FORM_FIELDS =
             setOf(EventFormField.Location, EventFormField.Description)
     }

app/src/main/java/de/jeanlucmakiola/calendula/domain/EventForm.kt

@@ -30,6 +30,17 @@ data class EventForm(
      * those are kept verbatim until the user picks something else.
      */
     val rrule: String? = null,
+    /**
+     * The event's own colour, or null to inherit the calendar's colour.
+     * [colorKey] is a `Colors.COLOR_KEY` from the calendar account's published
+     * event palette (Google, some CalDAV) — written as `EVENT_COLOR_KEY` so it
+     * round-trips through sync. When it is null but [color] is set, [color] is
+     * a raw ARGB written as `EVENT_COLOR` (local calendars, or synced ones the
+     * user opted into despite no palette). [color] mirrors the key's swatch when
+     * [colorKey] is set, so the picker can highlight it.
+     */
+    val colorKey: String? = null,
+    val color: Int? = null,
 )
 
 /**
@@ -43,6 +54,7 @@ enum class EventFormField {
     Recurrence,
     Availability,
     Visibility,
+    Color,
 }
 
 enum class EventFormProblem {
@@ -91,6 +103,11 @@ fun EventDetail.toEditForm(beginMillis: Long, endMillis: Long, zone: TimeZone):
         availability = availability,
         accessLevel = accessLevel,
         rrule = rrule?.removePrefix("RRULE:")?.takeIf { it.isNotBlank() },
+        // The provider fills EVENT_COLOR from the key, so [color] is the
+        // swatch either way; a null colour means the event inherits its
+        // calendar's colour.
+        colorKey = eventColorKey,
+        color = eventColor,
     )
 }
 
@@ -130,6 +147,7 @@ fun EventForm.populatedFields(): Set<EventFormField> = buildSet {
     if (rrule != null) add(EventFormField.Recurrence)
     if (availability != Availability.Busy) add(EventFormField.Availability)
     if (accessLevel != AccessLevel.Default) add(EventFormField.Visibility)
+    if (colorKey != null || color != null) add(EventFormField.Color)
 }
 
 fun EventForm.problems(): Set<EventFormProblem> = buildSet {

app/src/main/java/de/jeanlucmakiola/calendula/domain/Models.kt

@@ -58,8 +58,25 @@ data class EventDetail(
     val eventTimezone: String? = null,
     /** This device user's own response (`Events.SELF_ATTENDEE_STATUS`). */
     val selfStatus: AttendeeStatus = AttendeeStatus.Unknown,
+    /**
+     * The event's own raw colour (`Events.EVENT_COLOR`), null when the event
+     * inherits its calendar's colour. Unlike [EventInstance.color] (which
+     * already folds in the calendar fallback for display) this stays null so
+     * the edit form can tell "has own colour" from "inherits".
+     */
+    val eventColor: Int? = null,
+    /** The event's `Events.EVENT_COLOR_KEY` (a calendar-palette key), or null. */
+    val eventColorKey: String? = null,
 )
 
+/**
+ * One selectable event colour published by a calendar's account
+ * (`CalendarContract.Colors`, `TYPE_EVENT`): [key] is the account-scoped
+ * `COLOR_KEY` written as `EVENT_COLOR_KEY` (so the colour survives sync),
+ * [argb] is the swatch it renders as.
+ */
+data class EventColorOption(val key: String, val argb: Int)
+
 data class Attendee(
     val name: String,
     val email: String?,

app/src/main/java/de/jeanlucmakiola/calendula/ui/calendars/CalendarsScreen.kt

@@ -6,14 +6,10 @@ import android.content.Intent
 import android.provider.Settings
 import androidx.activity.compose.BackHandler
 import androidx.compose.foundation.background
-import androidx.compose.foundation.border
-import androidx.compose.foundation.clickable
 import androidx.compose.foundation.isSystemInDarkTheme
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
-import androidx.compose.foundation.layout.ExperimentalLayoutApi
-import androidx.compose.foundation.layout.FlowRow
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxSize
@@ -31,7 +27,6 @@ import androidx.compose.material.icons.automirrored.filled.ArrowBack
 import androidx.compose.material.icons.automirrored.filled.Notes
 import androidx.compose.material.icons.filled.Add
 import androidx.compose.material.icons.filled.CalendarMonth
-import androidx.compose.material.icons.filled.Check
 import androidx.compose.material.icons.filled.Close
 import androidx.compose.material.icons.filled.Delete
 import androidx.compose.material.icons.filled.Edit
@@ -73,8 +68,10 @@ import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import de.jeanlucmakiola.calendula.R
 import de.jeanlucmakiola.calendula.domain.CalendarSource
+import de.jeanlucmakiola.calendula.ui.common.CALENDAR_COLOR_PALETTE
 import de.jeanlucmakiola.calendula.ui.common.CalendarColorChip
 import de.jeanlucmakiola.calendula.ui.common.CollapsingScaffold
+import de.jeanlucmakiola.calendula.ui.common.ColorSwatchRow
 import de.jeanlucmakiola.calendula.ui.common.GroupedRow
 import de.jeanlucmakiola.calendula.ui.common.InlineTextField
 import de.jeanlucmakiola.calendula.ui.common.Position
@@ -325,7 +322,12 @@ private fun CalendarEditor(
                     color = MaterialTheme.colorScheme.onSurfaceVariant,
                 )
                 Spacer(Modifier.height(12.dp))
-                ColorPalette(selected = color, onSelect = { color = it }, dark = dark)
+                ColorSwatchRow(
+                    colors = CALENDAR_COLOR_PALETTE,
+                    selected = color,
+                    onSelect = { color = it },
+                    dark = dark,
+                )
             }
             EditorCard(
                 icon = Icons.AutoMirrored.Filled.Notes,
@@ -402,42 +404,6 @@ private fun EditorCard(
     }
 }
 
-@OptIn(ExperimentalLayoutApi::class)
-@Composable
-private fun ColorPalette(selected: Int, onSelect: (Int) -> Unit, dark: Boolean) {
-    FlowRow(horizontalArrangement = Arrangement.spacedBy(12.dp)) {
-        CALENDAR_COLOR_PALETTE.forEach { argb ->
-            val isSelected = argb == selected
-            // Show the pastel the calendar will actually render as, not the raw hue.
-            Box(
-                contentAlignment = Alignment.Center,
-                modifier = Modifier
-                    .padding(vertical = 4.dp)
-                    .size(40.dp)
-                    .clip(CircleShape)
-                    .background(pastelize(argb, dark))
-                    .then(
-                        if (isSelected) {
-                            Modifier.border(2.dp, MaterialTheme.colorScheme.onSurface, CircleShape)
-                        } else {
-                            Modifier
-                        },
-                    )
-                    .clickable { onSelect(argb) },
-            ) {
-                if (isSelected) {
-                    Icon(
-                        Icons.Default.Check,
-                        contentDescription = null,
-                        tint = Color.Black.copy(alpha = 0.7f),
-                        modifier = Modifier.size(20.dp),
-                    )
-                }
-            }
-        }
-    }
-}
-
 @Composable
 private fun AccountHeader(account: String, accountType: String) {
     val context = LocalContext.current
@@ -532,15 +498,3 @@ private fun curatedSourcePackage(accountType: String): String? = when {
     else -> null
 }
 
-/** Google-Calendar-style palette; values are ARGB ints for `Calendars.CALENDAR_COLOR`. */
-internal val CALENDAR_COLOR_PALETTE: List<Int> = listOf(
-    0xFFD50000, // red
-    0xFFE67C00, // orange
-    0xFFF6BF26, // amber
-    0xFF33B679, // green
-    0xFF0B8043, // dark green
-    0xFF039BE5, // blue
-    0xFF3F51B5, // indigo
-    0xFF8E24AA, // purple
-    0xFF616161, // graphite
-).map { it.toInt() }

app/src/main/java/de/jeanlucmakiola/calendula/ui/common/ColorSwatchRow.kt

@@ -0,0 +1,82 @@
+package de.jeanlucmakiola.calendula.ui.common
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.border
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.ExperimentalLayoutApi
+import androidx.compose.foundation.layout.FlowRow
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Check
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.unit.dp
+
+/**
+ * A wrapping row of round colour swatches; the one matching [selected] is
+ * ringed and checked. Shared by the calendar editor and the event-colour
+ * picker so both pick a colour the same way. Swatches render through
+ * [pastelize] — the softened colour the app actually paints, not the raw hue.
+ */
+@OptIn(ExperimentalLayoutApi::class)
+@Composable
+fun ColorSwatchRow(
+    colors: List<Int>,
+    selected: Int?,
+    onSelect: (Int) -> Unit,
+    dark: Boolean,
+    modifier: Modifier = Modifier,
+) {
+    FlowRow(modifier = modifier, horizontalArrangement = Arrangement.spacedBy(12.dp)) {
+        colors.forEach { argb ->
+            val isSelected = argb == selected
+            Box(
+                contentAlignment = Alignment.Center,
+                modifier = Modifier
+                    .padding(vertical = 4.dp)
+                    .size(40.dp)
+                    .clip(CircleShape)
+                    .background(pastelize(argb, dark))
+                    .then(
+                        if (isSelected) {
+                            Modifier.border(2.dp, MaterialTheme.colorScheme.onSurface, CircleShape)
+                        } else {
+                            Modifier
+                        },
+                    )
+                    .clickable { onSelect(argb) },
+            ) {
+                if (isSelected) {
+                    Icon(
+                        Icons.Default.Check,
+                        contentDescription = null,
+                        tint = Color.Black.copy(alpha = 0.7f),
+                        modifier = Modifier.size(20.dp),
+                    )
+                }
+            }
+        }
+    }
+}
+
+/** Google-Calendar-style palette; ARGB ints for a raw `CALENDAR_COLOR` / `EVENT_COLOR`. */
+val CALENDAR_COLOR_PALETTE: List<Int> = listOf(
+    0xFFD50000, // red
+    0xFFE67C00, // orange
+    0xFFF6BF26, // amber
+    0xFF33B679, // green
+    0xFF0B8043, // dark green
+    0xFF039BE5, // blue
+    0xFF3F51B5, // indigo
+    0xFF8E24AA, // purple
+    0xFF616161, // graphite
+).map { it.toInt() }

app/src/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditScreen.kt

@@ -41,6 +41,7 @@ import androidx.compose.material.icons.filled.Close
 import androidx.compose.material.icons.filled.EventAvailable
 import androidx.compose.material.icons.filled.Lock
 import androidx.compose.material.icons.filled.Notifications
+import androidx.compose.material.icons.filled.Palette
 import androidx.compose.material.icons.filled.Place
 import androidx.compose.material.icons.filled.Public
 import androidx.compose.material.icons.filled.Repeat
@@ -102,6 +103,7 @@ import de.jeanlucmakiola.calendula.R
 import de.jeanlucmakiola.calendula.domain.AccessLevel
 import de.jeanlucmakiola.calendula.domain.Availability
 import de.jeanlucmakiola.calendula.domain.CalendarSource
+import de.jeanlucmakiola.calendula.domain.EventColorOption
 import de.jeanlucmakiola.calendula.domain.EventFormField
 import de.jeanlucmakiola.calendula.domain.EventFormProblem
 import de.jeanlucmakiola.calendula.domain.RecurrenceEnd
@@ -110,6 +112,8 @@ import de.jeanlucmakiola.calendula.domain.RecurringWriteScope
 import de.jeanlucmakiola.calendula.domain.SimpleRecurrence
 import de.jeanlucmakiola.calendula.domain.parseSimpleRecurrence
 import de.jeanlucmakiola.calendula.domain.toRRule
+import de.jeanlucmakiola.calendula.ui.common.CALENDAR_COLOR_PALETTE
+import de.jeanlucmakiola.calendula.ui.common.ColorSwatchRow
 import de.jeanlucmakiola.calendula.ui.common.InlineTextField
 import de.jeanlucmakiola.calendula.ui.common.OptionCard
 import de.jeanlucmakiola.calendula.ui.common.currentLocale
@@ -414,6 +418,7 @@ private fun EventEditContent(
     var showReminderPicker by rememberSaveable { mutableStateOf(false) }
     var showRecurrencePicker by rememberSaveable { mutableStateOf(false) }
     var showVisibilityPicker by rememberSaveable { mutableStateOf(false) }
+    var showColorPicker by rememberSaveable { mutableStateOf(false) }
     var showFieldPicker by rememberSaveable { mutableStateOf(false) }
 
     val selectedCalendar = state.calendars.firstOrNull { it.id == form.calendarId }
@@ -423,6 +428,16 @@ private fun EventEditContent(
         ?: MaterialTheme.colorScheme.primary
     val gap = 12.dp
 
+    // Per-event colour applicability for the resolved calendar:
+    //  - palette calendars (Google, …) and local calendars always support it;
+    //  - synced calendars with no palette only when the user opted in, and even
+    //    then the colour may not survive the calendar's next sync (the warning).
+    val isLocalCalendar = selectedCalendar?.isLocal == true
+    val colorSupported = state.colorPalette.isNotEmpty() || isLocalCalendar ||
+        state.allowColorOnUnsupportedCalendars
+    val colorSyncRisk = state.colorPalette.isEmpty() && !isLocalCalendar &&
+        state.allowColorOnUnsupportedCalendars
+
     Column(
         modifier = modifier
             // Shrink the scroll viewport by the keyboard instead of letting
@@ -692,6 +707,67 @@ private fun EventEditContent(
             }
         }
 
+        OptionalFormSection(visible = EventFormField.Color in state.visibleFields) {
+            Spacer(Modifier.height(gap))
+            // The swatch the event will paint with: its own colour, else the
+            // calendar's. The Palette icon takes that colour as a preview.
+            val swatch = form.color ?: selectedCalendar?.color
+            EditCard(
+                icon = Icons.Default.Palette,
+                iconContentDescription = stringResource(R.string.event_edit_color),
+                iconTint = if (colorSupported && swatch != null) {
+                    pastelize(swatch, dark)
+                } else {
+                    MaterialTheme.colorScheme.onSurfaceVariant
+                },
+                onClick = { showColorPicker = true }.takeIf { colorSupported },
+            ) {
+                Row(
+                    verticalAlignment = Alignment.CenterVertically,
+                    modifier = Modifier.fillMaxWidth(),
+                ) {
+                    Column(modifier = Modifier.weight(1f)) {
+                        Text(
+                            text = stringResource(
+                                when {
+                                    !colorSupported -> R.string.event_edit_color_unsupported
+                                    form.color != null -> R.string.event_edit_color_custom
+                                    else -> R.string.event_edit_color_default
+                                },
+                            ),
+                            style = MaterialTheme.typography.titleMedium,
+                        )
+                        Text(
+                            text = stringResource(
+                                if (colorSupported) {
+                                    R.string.event_edit_color
+                                } else {
+                                    R.string.event_edit_color_unsupported_hint
+                                },
+                            ),
+                            style = MaterialTheme.typography.bodySmall,
+                            color = MaterialTheme.colorScheme.onSurfaceVariant,
+                        )
+                        if (colorSyncRisk) {
+                            Spacer(Modifier.height(2.dp))
+                            Text(
+                                text = stringResource(R.string.event_edit_color_sync_warning),
+                                style = MaterialTheme.typography.bodySmall,
+                                color = MaterialTheme.colorScheme.onSurfaceVariant,
+                            )
+                        }
+                    }
+                    if (colorSupported) {
+                        Icon(
+                            imageVector = Icons.Default.ArrowDropDown,
+                            contentDescription = null,
+                            tint = MaterialTheme.colorScheme.onSurfaceVariant,
+                        )
+                    }
+                }
+            }
+        }
+
         OptionalFormSection(visible = state.hiddenFields.isNotEmpty()) {
             Spacer(Modifier.height(20.dp))
             TextButton(
@@ -779,6 +855,28 @@ private fun EventEditContent(
         )
     }
 
+    if (showColorPicker) {
+        ColorPickerDialog(
+            palette = state.colorPalette,
+            selected = form.color,
+            hasExplicitColor = form.color != null,
+            syncWarning = colorSyncRisk,
+            onPickKey = { key, argb ->
+                viewModel.setColorKey(key, argb)
+                showColorPicker = false
+            },
+            onPickRaw = { argb ->
+                viewModel.setColorRaw(argb)
+                showColorPicker = false
+            },
+            onClear = {
+                viewModel.clearColor()
+                showColorPicker = false
+            },
+            onDismiss = { showColorPicker = false },
+        )
+    }
+
     if (showFieldPicker) {
         FieldPickerDialog(
             hiddenFields = state.hiddenFields,
@@ -1294,6 +1392,7 @@ private fun fieldLabel(field: EventFormField): Int = when (field) {
     EventFormField.Recurrence -> R.string.event_detail_recurrence
     EventFormField.Availability -> R.string.event_edit_availability
     EventFormField.Visibility -> R.string.event_edit_visibility
+    EventFormField.Color -> R.string.event_edit_color
 }
 
 private fun fieldIcon(field: EventFormField): ImageVector = when (field) {
@@ -1303,6 +1402,7 @@ private fun fieldIcon(field: EventFormField): ImageVector = when (field) {
     EventFormField.Recurrence -> Icons.Default.Repeat
     EventFormField.Availability -> Icons.Default.EventAvailable
     EventFormField.Visibility -> Icons.Default.Lock
+    EventFormField.Color -> Icons.Default.Palette
 }
 
 /**
@@ -1336,6 +1436,72 @@ private fun VisibilityPickerDialog(
     )
 }
 
+/**
+ * Event-colour picker: just the swatches. A non-empty [palette] (the calendar
+ * account's published colours) picks by key so the colour round-trips through
+ * sync; otherwise the app's own palette writes a raw colour, with a
+ * [syncWarning] when that calendar may not keep it. The "Reset" button (shown
+ * only once a colour is set) drops back to the calendar's own colour.
+ */
+@Composable
+private fun ColorPickerDialog(
+    palette: List<EventColorOption>,
+    selected: Int?,
+    hasExplicitColor: Boolean,
+    syncWarning: Boolean,
+    onPickKey: (String, Int) -> Unit,
+    onPickRaw: (Int) -> Unit,
+    onClear: () -> Unit,
+    onDismiss: () -> Unit,
+) {
+    val dark = isSystemInDarkTheme()
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text(stringResource(R.string.event_edit_color)) },
+        text = {
+            Column(verticalArrangement = Arrangement.spacedBy(12.dp)) {
+                if (palette.isNotEmpty()) {
+                    ColorSwatchRow(
+                        colors = palette.map { it.argb },
+                        selected = selected,
+                        onSelect = { argb ->
+                            palette.firstOrNull { it.argb == argb }
+                                ?.let { onPickKey(it.key, it.argb) }
+                        },
+                        dark = dark,
+                    )
+                } else {
+                    ColorSwatchRow(
+                        colors = CALENDAR_COLOR_PALETTE,
+                        selected = selected,
+                        onSelect = onPickRaw,
+                        dark = dark,
+                    )
+                    if (syncWarning) {
+                        Text(
+                            text = stringResource(R.string.event_edit_color_sync_warning),
+                            style = MaterialTheme.typography.bodySmall,
+                            color = MaterialTheme.colorScheme.onSurfaceVariant,
+                        )
+                    }
+                }
+            }
+        },
+        confirmButton = {
+            TextButton(onClick = onDismiss) { Text(stringResource(R.string.dialog_cancel)) }
+        },
+        dismissButton = if (hasExplicitColor) {
+            {
+                TextButton(onClick = onClear) {
+                    Text(stringResource(R.string.event_edit_color_reset))
+                }
+            }
+        } else {
+            null
+        },
+    )
+}
+
 private fun accessLevelIcon(level: AccessLevel): ImageVector = when (level) {
     AccessLevel.Default -> Icons.Default.Tune
     AccessLevel.Public -> Icons.Default.Public

app/src/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditUiState.kt

@@ -1,6 +1,7 @@
 package de.jeanlucmakiola.calendula.ui.edit
 
 import de.jeanlucmakiola.calendula.domain.CalendarSource
+import de.jeanlucmakiola.calendula.domain.EventColorOption
 import de.jeanlucmakiola.calendula.domain.EventForm
 import de.jeanlucmakiola.calendula.domain.EventFormField
 import de.jeanlucmakiola.calendula.domain.EventFormProblem
@@ -33,6 +34,18 @@ data class EventEditUiState(
      * then drops "only this event" (an exception row can't carry a rule).
      */
     val recurrenceChanged: Boolean = false,
+    /**
+     * The event-colour palette the resolved target calendar publishes; empty
+     * when it exposes none. Non-empty → the colour picker offers these swatches
+     * (written as a key, sync-safe); empty → see [colorMode].
+     */
+    val colorPalette: List<EventColorOption> = emptyList(),
+    /**
+     * Whether the user has opted into custom colours on calendars that publish
+     * no palette (a synced one may then drop the colour on sync). Mirrors the
+     * settings flag; ignored for local and palette-backed calendars.
+     */
+    val allowColorOnUnsupportedCalendars: Boolean = false,
 )
 
 /** One-shot state of a save request, mirroring DeleteUiState on the detail screen. */

app/src/main/java/de/jeanlucmakiola/calendula/ui/edit/EventEditViewModel.kt

@@ -12,6 +12,7 @@ import de.jeanlucmakiola.calendula.domain.AccessLevel
 import de.jeanlucmakiola.calendula.domain.Availability
 import de.jeanlucmakiola.calendula.domain.CalendarSource
 import de.jeanlucmakiola.calendula.domain.EditSnapshot
+import de.jeanlucmakiola.calendula.domain.EventColorOption
 import de.jeanlucmakiola.calendula.domain.EventForm
 import de.jeanlucmakiola.calendula.domain.EventFormField
 import de.jeanlucmakiola.calendula.domain.RecurringWriteScope
@@ -19,12 +20,17 @@ import de.jeanlucmakiola.calendula.domain.populatedFields
 import de.jeanlucmakiola.calendula.domain.problems
 import de.jeanlucmakiola.calendula.domain.toEditSnapshot
 import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.catch
 import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.distinctUntilChanged
+import kotlinx.coroutines.flow.flatMapLatest
+import kotlinx.coroutines.flow.flow
 import kotlinx.coroutines.flow.flowOn
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.stateIn
@@ -98,19 +104,44 @@ class EventEditViewModel @Inject constructor(
         val writable: List<CalendarSource>,
         val lastUsed: Long?,
         val defaultFields: Set<EventFormField>,
+        val allowColorOnUnsupported: Boolean,
     )
 
+    /** Writable calendars — the only valid event targets. */
+    private val writableCalendars: Flow<List<CalendarSource>> = repository.calendars()
+        .map { calendars -> calendars.filter { it.canModifyContents } }
+        .catch { emit(emptyList()) }
+
+    /** The target calendar id, resolved exactly as the form shows it. */
+    private val resolvedCalendarId: Flow<Long?> = combine(
+        _form.map { it?.calendarId },
+        writableCalendars,
+        prefs.lastUsedCalendarId,
+    ) { picked, writable, lastUsed ->
+        picked
+            ?: lastUsed?.takeIf { id -> writable.any { it.id == id } }
+            ?: writable.firstOrNull()?.id
+    }.distinctUntilChanged()
+
+    /** The resolved calendar's published event palette, refetched when it changes. */
+    @OptIn(ExperimentalCoroutinesApi::class)
+    private val colorPalette: Flow<List<EventColorOption>> = resolvedCalendarId
+        .flatMapLatest { id ->
+            flow { emit(id?.let { repository.eventColorPalette(it) }.orEmpty()) }
+        }
+        .flowOn(io)
+
     val state: StateFlow<EventEditUiState?> = combine(
         combine(_form, _saveState, _showProblems, _revealed, _editTarget, ::LocalInputs),
         combine(
-            repository.calendars()
-                .map { calendars -> calendars.filter { it.canModifyContents } }
-                .catch { emit(emptyList()) },
+            writableCalendars,
             prefs.lastUsedCalendarId,
             settingsPrefs.defaultFormFields,
+            settingsPrefs.allowColorOnUnsupportedCalendars,
             ::ExternalInputs,
         ).flowOn(io),
-    ) { local, external ->
+        colorPalette,
+    ) { local, external, palette ->
         val form = local.form ?: return@combine null
         val resolvedId = form.calendarId
             ?: external.lastUsed?.takeIf { id -> external.writable.any { it.id == id } }
@@ -129,6 +160,8 @@ class EventEditViewModel @Inject constructor(
             // the scope dialog drops "only this event" after a rule change.
             recurrenceChanged = local.editTarget != null &&
                 resolved.rrule != local.editTarget.original.rrule,
+            colorPalette = palette,
+            allowColorOnUnsupportedCalendars = external.allowColorOnUnsupported,
         )
     }
         .stateIn(
@@ -207,10 +240,25 @@ class EventEditViewModel @Inject constructor(
     fun setLocation(value: String) = update { it.copy(location = value) }
     fun setDescription(value: String) = update { it.copy(description = value) }
     fun setAllDay(value: Boolean) = update { it.copy(isAllDay = value) }
-    fun setCalendar(id: Long) = update { it.copy(calendarId = id) }
+
+    /**
+     * Switching calendars drops any chosen colour: a palette key is
+     * account-scoped, and a raw colour may be invalid on the new calendar.
+     * The event falls back to the new calendar's colour until re-picked.
+     */
+    fun setCalendar(id: Long) = update { it.copy(calendarId = id, colorKey = null, color = null) }
     fun setAvailability(value: Availability) = update { it.copy(availability = value) }
     fun setAccessLevel(value: AccessLevel) = update { it.copy(accessLevel = value) }
 
+    /** Pick a palette colour (round-trips via its key); [argb] is its swatch. */
+    fun setColorKey(key: String, argb: Int) = update { it.copy(colorKey = key, color = argb) }
+
+    /** Pick a raw colour (local / opted-in calendars), clearing any palette key. */
+    fun setColorRaw(argb: Int) = update { it.copy(colorKey = null, color = argb) }
+
+    /** Clear the colour so the event inherits its calendar's. */
+    fun clearColor() = update { it.copy(colorKey = null, color = null) }
+
     /** Bare RRULE value from the recurrence picker; null = does not repeat. */
     fun setRecurrence(rrule: String?) = update { it.copy(rrule = rrule) }
 

app/src/main/java/de/jeanlucmakiola/calendula/ui/settings/SettingsScreen.kt

@@ -431,6 +431,27 @@ private fun EventFormScreen(
                 onClick = { viewModel.setFormFieldDefault(field, !checked) },
             )
         }
+
+        // Per-event colour on calendars that publish no colour set (some
+        // CalDAV) — off by default, with the honest caveat that the colour may
+        // not survive their next sync. Local and palette calendars ignore it.
+        Spacer(Modifier.height(24.dp))
+        GroupedRow(
+            title = stringResource(R.string.settings_color_unsupported),
+            summary = stringResource(R.string.settings_color_unsupported_hint),
+            position = Position.Alone,
+            trailing = {
+                Switch(
+                    checked = state.allowColorOnUnsupportedCalendars,
+                    onCheckedChange = { viewModel.setAllowColorOnUnsupportedCalendars(it) },
+                )
+            },
+            onClick = {
+                viewModel.setAllowColorOnUnsupportedCalendars(
+                    !state.allowColorOnUnsupportedCalendars,
+                )
+            },
+        )
     }
 }
 
@@ -555,6 +576,7 @@ private fun formFieldLabel(field: EventFormField): Int = when (field) {
     EventFormField.Recurrence -> R.string.event_detail_recurrence
     EventFormField.Availability -> R.string.event_edit_availability
     EventFormField.Visibility -> R.string.event_edit_visibility
+    EventFormField.Color -> R.string.event_edit_color
 }
 
 @Composable

app/src/main/java/de/jeanlucmakiola/calendula/ui/settings/SettingsUiState.kt

@@ -20,4 +20,9 @@ data class SettingsUiState(
     val defaultFormFields: Set<EventFormField> = SettingsPrefs.DEFAULT_FORM_FIELDS,
     /** Whether Calendula posts reminder notifications (v1.4). */
     val remindersEnabled: Boolean = true,
+    /**
+     * Whether the event-colour picker is offered on calendars that publish no
+     * colour palette (the colour may then not survive their next sync).
+     */
+    val allowColorOnUnsupportedCalendars: Boolean = false,
 )

app/src/main/java/de/jeanlucmakiola/calendula/ui/settings/SettingsViewModel.kt

@@ -24,20 +24,27 @@ class SettingsViewModel @Inject constructor(
 
     val state: StateFlow<SettingsUiState> =
         combine(
-            prefs.themeMode,
-            prefs.dynamicColor,
-            prefs.weekStart,
-            prefs.defaultFormFields,
-            prefs.remindersEnabled,
-        ) { theme, dynamic, weekStart, formFields, reminders ->
-            SettingsUiState(
-                themeMode = theme,
-                dynamicColor = dynamic && dynamicColorAvailable,
-                dynamicColorAvailable = dynamicColorAvailable,
-                weekStart = weekStart,
-                defaultFormFields = formFields,
-                remindersEnabled = reminders,
-            )
+            // combine() only types up to five flows, so the sixth pref folds
+            // into the assembled state in an outer combine.
+            combine(
+                prefs.themeMode,
+                prefs.dynamicColor,
+                prefs.weekStart,
+                prefs.defaultFormFields,
+                prefs.remindersEnabled,
+            ) { theme, dynamic, weekStart, formFields, reminders ->
+                SettingsUiState(
+                    themeMode = theme,
+                    dynamicColor = dynamic && dynamicColorAvailable,
+                    dynamicColorAvailable = dynamicColorAvailable,
+                    weekStart = weekStart,
+                    defaultFormFields = formFields,
+                    remindersEnabled = reminders,
+                )
+            },
+            prefs.allowColorOnUnsupportedCalendars,
+        ) { base, allowColor ->
+            base.copy(allowColorOnUnsupportedCalendars = allowColor)
         }.stateIn(
             scope = viewModelScope,
             started = SharingStarted.WhileSubscribed(5_000L),
@@ -63,4 +70,8 @@ class SettingsViewModel @Inject constructor(
     fun setRemindersEnabled(enabled: Boolean) {
         viewModelScope.launch { prefs.setRemindersEnabled(enabled) }
     }
+
+    fun setAllowColorOnUnsupportedCalendars(enabled: Boolean) {
+        viewModelScope.launch { prefs.setAllowColorOnUnsupportedCalendars(enabled) }
+    }
 }