Mac curiousity . :D curious about the color of the macbook after a few months/years?

i've seen the macbook on display in a store and its trackpad was kinda grayish. somewhat far from the original color of the trackpad. i was just wondering what brought this color to the trackpad. and if it would soon happen to most trackpads how long does it usually take before the color turns to a grayish color? thanks!