Here’s a process I was previously unaware of… the use of easily available hydrogen peroxide-based consumer products and ultraviolet light (or just sunlight) to restore the original bright white color of old plastic. While the guy doing the video focuses on old computer equipment, this process might be of particular interest for old unpainted display models and the like that have turned yellow or brown due to UV exposure over the years or decades.
Something I don’t know: does this process restore the structural properties of the old plastic? With years of UV damage, not only does white plastic turn yellow, it also becomes brittle. While I really rather doubt it, I suppose it might be just barely possible that this process will reverse that embrittlement. And if it works on plastic, what else might it de-yellow? Paint? Paper? Hmmm…