One way that a marker color can be changed is with a trigger.
Setup the marker with a name and text.
Set up a trigger to activate with blufor / opfor or what ever you want. Also, select if it will be repeated or not. Then in the on ACT. field enter the following:
"markerName" setMarkerColorLocal "ColorGreen";
You could also have the trigger call a script to do this also(though I'm a bit rusty with scripting).