/**
  * Get already used colors by user.
  * @param User $user
  * @return array
  */
 public static function getAlreadyUsedColorsByUser(User $user)
 {
     $savedCalUsedColors = CalendarUtil::getUsedCalendarColorsByUser($user, 'SavedCalendar', 'createdByUser');
     $sharedCalUsedColors = CalendarUtil::getUsedCalendarColorsByUser($user, 'SavedCalendarSubscription', 'user');
     return CMap::mergeArray($savedCalUsedColors, $sharedCalUsedColors);
 }