iCloud: Change a calendar’s name or color in iCloud
You can assign a different color to each calendar you create using Calendar on iCloud.com so you can easily tell which calendar an event belongs to.
You can edit a calendar’s name and color at any time. When you change a calendar’s color, all of its events change to the new color.
Click Edit below the sidebar.
Do any of the following:
Change a calendar’s name: Double-click the calendar’s name and type a new name.
Change a calendar’s color: Click the Color button next to the calendar’s name, then choose a color.
Note: Changes you make appear on every device that has iCloud Calendar turned on. You can’t change the name or color of the Birthdays calendar. Color changes aren’t visible in Microsoft Outlook.