HI, As for un-yellowing plastic (ie, your mouse) You should really check out RetroBrite (just Google it) Even though I didn't have concentrated H2O2, it lightened an Amiga trackball of mine by several shades.
I also agree with save2600 about the Novus plastic polishes. Of course, they won't un-yellow plastic, but if the color is actually dirt or grime of some sort, the Novus stuff is great. I bought a C128 at a resale shop that was positively nasty looking
A few applications of Novus # 2 made it look much better.
Oh, the yellowing occurs as a side-effect of the fire-retardants in the plastic. I may be wrong, but I think that there isn't anything to stop the yellowing permanently, short of using the RetroBrite method.
my 2 kopeks....
