I have to say that my iPad 3 had this issue (a kind of yellow shading on the left). When they first came out it was worse but did get a bit better the first week or so so I kept it. I really thought I would get used to it but I never did. Every time I was on this site, in a Notes app (that has a lot of white), any site with a lot of white, I saw it. I even changed both iBooks and my kindle app to a black background to get away from it.
I gave that one to my grandson who doesn't care because he's never on a really white page. I never updated it to iOS 7. I can imagine just how much it would have bothered me with all the white in iOS 7.
My recommendation - if it bothers you now don't count on 'getting used to it'. You might not and with the new OS it will be worse than on iOS 6.
That being said, my new iPad Air has a great screen, completely even color, no shadows, very nice. I'm going to enjoy it a lot more than I did that iPad 3.