Well, I've just put a blue LED in my mouse - not the illumination LED, but the tracking LED that gets brighter when you run your finger over the sensor. So it does work then - I did wonder, but it's nice to know. Is there any need to write a how-to? All you do is take your mouse apart, desolder the red LED and solder a blue LED in place the same way round. Simple Oh yeah, the mouse I tried it with is a Trust ami mouse 2505 mini optical. I might just put a blue LED in my intellimouse though as it's a success with this one.