Ah, I just meant it to be a purely for looks. My friend and I did a case mod a while back with some cold cathodes. The blue lights were on by default and deactivated by sound, while the red would activate on loud sounds. (Mainly explosions and deep bass) It looked kinda cool to show off, but it got distracting in the dark since it would flash a lot.
*edit* Some mice are completely IR or at least don't require visible light to track. I know that I just got my Razer Lachesis (which is pretty sick btw) and I was surprised to see that there was no light coming from the bottom.