To change the color of your event:
Go to the Wix Editor page.
Open the Calendar settings.
Click on Manage Events.
Click on the event.
Select Edit.
Change the color in the Color section.
If you have assigned a category to the event, the event will take the color of the category.
Please note that in case of synced events, the events synced from an external calendar, such as Google and Outlook, can only be edited on the original calendar. So, to change the color of synced events, go to the settings of the original calendar.