I have a 1999 GS300 with a problem. Thw white paint on the cladding and bumpers has turned yellowish.

Has this happened to anybody else?

 

I have seen this happen before unfortunately there really isn't anything you can do. Basically what has happened is your paints pigment has yellowed. You may want to check with your Lexus dealer and see if there is anything they can do for you under warranty. Only fix is repaint