Why aren't my event colors changing?

In Calendar Op.2, each event takes the color of the calendar it belongs to, exactly as set in the built-in iOS Calendar. Colors aren’t set per individual event.

To use different colors, organize your events into separate calendars:

1. In the built-in Calendar app, create or choose a calendar and set its color (tap Calendars → ⓘ → pick a color).
2. Assign each event to the calendar whose color you want.

Those colors then appear in Calendar Op.2 automatically.