After sitting down and thinking about whether or not you could change the LED in an optical mouse to something other than the standard red that they usually are, I decided to test the theory. After a quick check online for info on the topic, it seems as though it has been attempted before. Blue works well and mice with a blue LED are already available anyway. Green can be a problem on some surfaces although I don't have any problem using green in my current mouse. Allegedly infra-red LED's will work quite well if you want a mouse with no visible light. Even UV has been proven to work.
Once you get your mouse open (finding hidden screws is a bitch), you will find a regular old 5mm red or possibly blue LED on the board next to the optical sensor. This mod is as simple as de soldering the LED and soldering in an LED of your colour choice in its place.