I'm saying this merely from personal experience. I had an iPad 3 that was very noticeably pink on the bottom half. I showed it to my roommate, who immediately said "Why does your screen look so pink?" His girlfriend, on the other hand, had no idea what we were talking about. Neither did my parents, and neither did any of my other friends. It seems that many people just don't notice or care about that kind of blotchiness? I really don't know, it's my only explanation.
I've seen the same problem in most of the units at Best Buy, the Apple Store, etc. Almost all of them have it, but it seems like the majority of people don't notice it or aren't bothered by it. And no, I'm not just OCD, because iPad 2 screens all look uniform white to me and I've never had a problem with Apple's screens before.
It's something to do with the new Samsung retina displays...each iPad 3 is different, with its own "special" yellow/pink/cyan mottled color scheme.
If you don't see the discolouration -- be happy! I'm happy for you that you get to enjoy your device worry-free. I think iPad 3 is an excellent product otherwise.