How to Customize Colors
You can add colors and effects individually to each day, to a group of days, or to all of them.
Simply highlight the days you wish to color, select Fill from the Home tab, and choose a color.
For a more color-coordinated calendar, begin by choosing a Theme in the Home tab to select a color scheme.
Then, instead of choosing a fill, choose a Quick Style from the Home tab to add preset styles that include color, font, line style, effects, and more.