I found how to get rid of it!!! i just used lemon cream clenser and now its white again, the whole thing, not just the L, R buttons
Google it, a lot of people have been having a problem where there Polar White DS Lites have been turning a bit yellowish, same with the new apple macbooks apparantly, i had the problem, i tried bleech and it didnt work, so i tried the Cream clenser that i fond in the laundry. It took the yellow right out!
wow it does seem like many people have had this problem. i still enjoy my classic silver ds. got it the first month releasing the ds too =]. just a few dents here and there because of throwing it across the room after trying to nail down snaking on mario kart lol! anyways, looks like you should share your discovery with others because i read like countless posts on other websites about it.
