I think cazabam was referring to the palmrest. He may have said "keyboard" because it's all one unit-- keyboard, mouse pad, mouse button, and palm rest.

The problem was that the palmrest turned yellow. My MacBook was built in June, and the mouse button went out just about the same time as the wrist rest area turned yellow. This was in early September. I went to my local Apple Store and they fixed it on site within 24 hours.

I can't tell from your photo, but it doesn't look yellow-- it looks smudged with blue or something. The best suggestion I have is the one Extreme had-- go visit the Genius Bar at your local Apple Store.