When you create an event, select "Calendar" at the top. Then tap the "Create new calendar" button to create a calendar.
Try creating a calendar for each type of event.
For example, create categories such as "Hobbies" or "Work", and set a color for each calendar.
After that, when you create an event, simply choose the calendar you created and the event will take on that color.
For example, enter "Watch a soccer game" as the event title, select the "Hobbies" calendar you created, and save.
How to change the color of a calendar you created
Tap "Add/Edit calendar" on the settings screen, select the calendar you want to change, choose the color you like, and tap the "Done" button at the top right to finish.