my faceplate just turn to yellowish white

how i can make it white again any suggestion?
What, like overnight? Do you mean the pickguard?

Some folks pay a lot of extra cash to get this aged look. (A practice at which I laugh: Ha ha!)
Quote by BK202
Acid has been causing problems on this thread for a while. He just likes attention because he never got/gets enough from his parents or something.
Run it through the washing machine with bleach. Seriously do not worry about it. Plastic changes color over time and is nothing to worry about. Unless it is one of the older plastics that degrade into a substance that is pretty close to nitro glycerin and can explode.

The following statement is true. The proceeding statement is false.
^^ UV Damaged then, I don't think there's anything you can do about it now.
Moving on.....
fortunately for you pickguards are cheap i don't think there's a whole lot you can do to bring one back from yellowing.
Warmoth Telecaster Deluxe. Warmoth Strat. Seagull Artist Portrait Acoustic.

"Well good God damn and other such phrases, I haven't heard a beat like this in ages!"
-Dan Le Sac Vs The Scroobius Pip