I have an old flat white colored pickguard from my first guitar that I got signed by some guitarists I like with permanent marker. However, with age, the plastic has yellowed somewhat, which normally wouldn't be a problem (it's a nice cream color right now), except now I'd like to have the pickguard framed, and there are parts of it which were covered by the knobs of the guitar that didn't get stained, and I'd like it to all be a consistent color.
I've heard that you can soak yellowing plastic in hydrogen peroxide, and set it out in sunlight for a bit to restore it to its original color, but I'm concerned that this, and other methods like bleaching the pickguard might also remove the signatures on it. Thus, I was wondering if anyone knew a method that would let me restore the color of the original plastic without removing the signatures.