From a M@C site, a possibly adventurous fix for yellowing: sounds like it could work. Fortunately my A500 is pretty clean yet.... so I haven't tried it myself:
How can I get rid of that ugly yellowing on my M@c's case?
This procedure seems to work to lighten the yellowing pretty well (though it won't completely get rid of it):
* Get some Clorox Outdoor Cleaner and a spray bottle.
* Dilute one part Clorox with two parts water and put it in the spray bottle
* Disassemble the M@c.
* On a sunny day (sorry, Seattle and London folks, but you'll just have to work with what you've got), put the plastic front and back outside and spray them with the Clorox solution.
* Allow to dry (ideally in direct sun) and repeat up to four times.
* Wipe everything thoroughly after the last drying to remove the residue. A soft-scrub sponge used for Teflon frying pans works well for this.
* (optional) Finish it off with a coat of Scott's Liquid Gold so the shine comes back.
If you can find Clorox Cleanup Gel, use that instead of Outdoor Cleaner. It's gentler to the plastic and gives a lighter bleaching.
Keep the M@c away from UV light (including fluorescents) and sources of smoke and ozone to keep the yellowing from coming back.
