- Change the calendar color on the server
- Refresh your calendar list (DAVdroid / Choose account / Refresh calendars). The new color is now be shown in the collection list.
- At every calendar sync, colors will be written to the actual local calendars. Force synchronization to apply the color immediately.
If you don't want the calendar colors to be kept in sync with your collection list: DAVdroid / Account settings / disable "Manage calendar colors". In this case, you can set the colors manually (see below).
- Add your calendars as usual, check them in DAVdroid and synchronize. They're now visible in your calendar app, but in "DAVdroid green".
- DAVdroid / Choose account / Account settings / disable "Manage calendar colors". This will prevent DAVdroid from updating the calendar colors at every sync.
- Use a third-party app like Calendar Color (F-Droid) or Calendar Colors (Play Store) to set the calender colors.