Version 11.3 improves how dates are colored in the Date Navigation Pane and Mini Calendar to be based on the order of calendars in the calendar list, rather than always using the color of the first event on the date. Calendars at the top of the list will now have color priority over calendars lower in the list, regardless of the event starting times.
Here's a simple example. Nov 1 contains two events. Notice the date is colored blue in the Date Navigation Pane, which corresponds to the color of the first calendar in the list.
To re-order the calendar list, click and drag a calendar to the desired location. A black line will show where the calendar will be inserted. Release the mouse button to complete the move.
Notice the color of November 1 changed after the calendar list was re-ordered.