properly update event type color

- before updating the color, check if the color has a key
- if it does, we update the CALENDAR_COLOR_KEY column (which will also update the CALENDAR_COLOR column internally)
- if it does not have a key (ie, if it is not a defined color), we update the CALENDAR_COLOR column and set the CALENDAR_COLOR_KEY to empty string
- one note here is that transparent color (0) is not usually a defined color and setting CALENDAR_COLOR to 0 can cause some Calendar apps (like Google Calendar) to convert this to black color (#FF00000).

app/src/main/kotlin/com/simplemobiletools/calendar/pro/helpers/CalDAVHelper.kt

@@ -85,22 +85,37 @@ class CalDAVHelper(val context: Context) {
         return calendars
     }
 
-    // check if the calendars color or title has changed
     fun updateCalDAVCalendar(eventType: EventType) {
-        val uri = Calendars.CONTENT_URI
-        val newUri = ContentUris.withAppendedId(uri, eventType.caldavCalendarId.toLong())
+        val uri = ContentUris.withAppendedId(Calendars.CONTENT_URI, eventType.caldavCalendarId.toLong())
         val values = ContentValues().apply {
-            put(Calendars.CALENDAR_COLOR, eventType.color)
+            val colorKey = getCalDAVColorKey(eventType)
+            if (colorKey != null) {
+                put(Calendars.CALENDAR_COLOR_KEY, getCalDAVColorKey(eventType))
+            } else {
+                put(Calendars.CALENDAR_COLOR, eventType.color)
+                put(Calendars.CALENDAR_COLOR_KEY, "")
+            }
             put(Calendars.CALENDAR_DISPLAY_NAME, eventType.title)
         }
+
         try {
-            context.contentResolver.update(newUri, values, null, null)
+            context.contentResolver.update(uri, values, null, null)
             context.eventTypesDB.insertOrUpdate(eventType)
         } catch (e: IllegalArgumentException) {
             e.printStackTrace()
         }
     }
 
+    private fun getCalDAVColorKey(eventType: EventType): String? {
+        val colors = getAvailableCalDAVCalendarColors(eventType)
+        val colorKey = colors.indexOf(eventType.color)
+        return if (colorKey > 0) {
+            colorKey.toString()
+        } else {
+            null
+        }
+    }
+
     @SuppressLint("MissingPermission")
     fun getAvailableCalDAVCalendarColors(eventType: EventType): ArrayList<Int> {
         val colors = SparseIntArray()