Couple of things I've found in my experiments with H2O2:

Blue, red and purple plastics (maybe others) tend to bleach if left in too long - an hour or two in a jar of 35% strength in the sun is plenty.

35% H2O2 doesn't seem to damage stickers, bizarrely. I've chucked a few G1 figures in the good stuff for several hours and found it's had little to no affect on the decals, when I was expecting them to turn to mush.