Hi there, After buying a new case for my 4S, I realized that my White 4S was a turning a bit yellow. Compared to the bright white of the case, my iPhone looked really yellow. It was horrific, you could clearly tell the difference in color. Is there a reason for this? Or should I have just bought the black one instead? *Note, my iPhone is more than 2 years old. I got it in Dec '11.