Check out the following steps to change the color of your Calendar events.
Tap + to create a new event.
Tap the color icon on the next screen
Tap the color you’d like to use for this event. You may also set this color as your Calendar’s default color by tapping Set to default calendar color.
After editing all the necessary details of your event, tap the check icon to save and exit. Your chosen color is now reflected as a colored bar on your Calendar’s monthly view and within the event screen.
Note: You can only sync the color of events created via a Google account.