Calendar tasks can be color-coded, just like for the Gantt module. When heatmap mode is off, there is no color coding:
Activating the Heatmap mode
To activate the Heatmap mode you can use the 
shortcut.
Go to View dropdown and click on Heatmap mode.
A checkmark indicates whether the Heatmap mode is currently:
ON |  |
OFF |  |
Task Color
Task color can be displayed based on:
Task status
Manually selected colors
Task status
tasks status
grey (TO DO)
blue (IN PROGRESS)
green (DONE)
Manually selected colors
Below you can see how manual colors translate to the Calendar module:
You can change the task color directly in the Calendar module. Right-click on a task to see a pop-up menu. The selected task will be highlighted in blue.
Once you have selected a color click outside of the pop-up menu to close it. The task is no longer highlighted and a new color is visible.
You can change the manually selected task colors, even when the Heatmap mode is inactive. The pop-up menu is still accessible and changes can be made. Changes made to the manual task color will affect other modules (Gantt).