Can we change the color of KML overlay?

Using Flight Plan->Map Tool->KML Overlay, I was able to import a KML file into Mission Planner.

Is there a way to change the color of the purple circles?

Nope, only in the code and recompile.

So, you mean I would have to change something in the source code of Mission Planner?

Yes.
Actually it is in FlighPlanner.cs line 1006

Awesome! Thanks for your help.