retrobright?

[rybett]

Can somepony with more experience google this stuff and see if it would work on ponys? 
Dave has used it on old video game stuff and it was amazing, just unsure about the critters.   

[babystarz]

Based on what I'm seeing about the ingredients in this product, the main agent is hydrogen peroxide and the process for using it is very similar to a combination of sunfading and a hydrogen peroxide/oxyclean bath. So I assume the same rules would apply as for those procedures, namely, the product should not go on pony hair unless you're willing to sacrifice the hair (and NO tinsel or color-changing hair), and it will lighten plastic, so white ponies would be best to use this with, and a test spot on colorful ponies would be in order before covering them in it to be sure it won't bleach them. And it should probably be kept off symbols if you're going to leave the gel on the pony for any longer than a few minutes. It will probably work well on overall brightening, as well as stains and spots from mold and markers. It's also important to check on a pony at regular intervals to see the progress the gel is making and to not let it go overboard

[Diamond]

Hmm I wonder if it would work on yellowed Breyer plastic?

[BlackCurtains]

Retr0bright is specifically for ABS plastics that contain bromine so I don't think it would work on ponies. It never hurts to try though