Calendar Colors in Outlook

 If more than one calendar is displayed, color-coding is a way to easily identify which calendar you are viewing.  
 
To change colors, simply right-click on the calendar and select color.
Suppose you want to make sure you don't have conflicts between the two calendars. With overlay mode you can do just that; overlay mode allows you to see how multiple schedules look as one.

1. Check the boxes of the calendars you want to view in Overlay mode.
2. Right-click on any of the calendars
3. Click Overlay from the menu and the calendars will automatically switch to overlay mode with their respective colors still attached.