On a similar note, I've had a lot of luck at using Magic Eraser to remove the old lacquer that yellows over time. It takes awhile and you have to be careful not to remove the original ink. However the playfield regains a lot of its original brighter true color. You must clearcoat the playfield however to prevent it from wearing quickly.
To match the yellowed whites, try mixing a little bit of yellow, brown, black, or combination of the two to your base white. Another color may be needed to help match it as well.