I googled this recently and found claims for just about everything. lol I try not to use anything with bleach on plastic because over a period of time, it will make it brittle.
I found one website that claimed peroxide will whiten the plastic. I thought, what the heck, I have a bottle in the cabinet, I'll give it a try. The shower in our trailer was almost orange in places. The original owners had never removed a label on the shower wall with information and cleaning instructions for the shower. Oddly enough, it didn't say to keep the skylight covered to prevent yellowing. When I removed that label, it left a perfectly white square in the middle of the yellow.
Anyway, I put peroxide in a spray bottle, cleaned the shower to remove any soap residue and sprayed it down with peroxide. The directions online said to leave it 15-30 minutes and may have to repeat. That may have been good instructions for a slightly yellowed shower, but not an almost orange one. Actually, only the tops of the corner shelves were orange, everything else was just yellowed. The tub was still white, and the buttons covering the screws. Everything else in the shower was varying shades of yellow. The sink was even yellow and it wasn't under the skylight at all.
After 15 minutes, I looked at it, couldn't see any difference, and sprayed it again. After another 30 minutes, I wiped it down and could tell it was less orange. For a week, I sprayed it every day and by the end of that week, the orange was gone, the edges of the white square weren't as defined, and the sink was white again.
When we sold the trailer, the shower looked pretty good. Not great. Not white. But pretty good. I think with enough time, it might have whitened the whole thing.