When a new Plan is applied to a calendar it is assigned a color. This makes it easy to decipher one Plan from another, and to determine which Plan an Activity is associated with.
In the image above you will see:
(A) You have control over the Plan's color in the Plan Panel
(B) The color associated with the Plan is shown in the Timeline next to the Plan's name
(C) When an Activity on the calendar is associated with the Plan, you will see the Plan's color to the left of the Activity
Plan Templates also have a color, allowing you to pre-determine the color used when the Plan is applied.
As always, don't hesitate to get in touch with any questions using the support chat below.