The color is changed by placing another marker in front of the original one.
The coloring markers are plain with no transparent nor imagemap and defined {clickable:false}. They dont have a shadow.
That kind of marker passes clicks and mouseovers to the fully equipped original marker that lies behind.
This technique was published a few hours before .setImage() method was released in Google Maps API.
Map is panned back to original center by 'infowindowclose' GEvent
An alternative solution to undocumented {suppressMapPan:true} option