Activated Hotspots

Not sure if I'm asking a basic question or trying to achieve the impossible! Here goes anyway.
I'm trying to build a Virtual Tour which will contain an image map. Is it possible to be able to change the hotspot colour after the viewer has activated/visited the hotspot.
What I'm trying to achieve is to show the viewer which hotspots have been selected and viewed, and which have not.
Is there a simple solution to this. any pointers would be very helpful.
Many thanks
Graham

Many thanks Sacha, it is a floorplan that I'm attempting to do it on.
I'm away now to attempt it.
Cheers Graham