I recently picked up a used 2011 21.5 inch iMac and after using it for about a week I have noticed that the bottom half of the screen is yellower than the top half. It isn't terrible but enough that I notice it. I was wondering if anyone else experienced this. The computer does have 2 months of the original warranty left so I'm wondering if I should take it into the Apple Store. Will Apple give me a hard time if I was not the original purchaser, or as longer as there is warranty left is that all that matters? Thanks.