Discoloration on the aluminum macbooks

Hello, has anyone noticed any discoloration on their new aluminum macbooks? When I first opened my macbook and got through the packaging I was two excited to notice anything. But after about three days I noticed a discoloration the size of a thumb print slightly below the power button. Then I started to notice more discolorations in better light and I don't think that it was from me because of been extremely careful and annul for that matter about using it. Has anyone else noticed this or have any advice for this. I could bring it into an apple store, but I wanted to know if this is a common problem, since I also paid $300 dollars more, partially for the better physical design and chassis of the aluminum macbook over the white one.