You can change the colors of your events by using the "Highlight" feature in the Event Editor, Event Tags, and Calendar Overlays. You can also add a border to your events and choose a custom color for that border. This can make it easier to distinguish between different events in your calendar or you can use it to add an extra layer of color-coding to your events.
The border options listed from top to bottom are no border, thin border, and left border. You can see what it will look like in different calendar views below:
To learn how to add a border to your events follow the steps in the image below:
While you can choose to add a border to events in your calendar, you can also choose to add a border to Event Tags and add a border to events from Calendar Overlays. See the image below: