In order not to confuse the stored reminders for appointments and events in the Calendar app on the OnePlus smartphone, we can assign an individual color to each appointment category of the different Google Accounts.

Note: This includes, for example, birthday reminders.

Android 10 | OxygenOS 10.0
Step 1:  Open the  Calendar app
Step 2:  Open the  menu
Step 3:  Open the  Settings
Step 4:  Choose a  category
Step 5:  Tap on  Color
Step 6:  Choose a  color
  1. Open the Calendar app
  2. Open the menu
  3. Open the Settings
  4. Choose a category
  5. Tap on Color
  6. Choose a color

OnePlus Instructions