My first 64g AT&T unit had top 1/3 (portrait) so yellow that one side of keyboard keys were tannish and other side gray. Also somewhat dim. Called Apple Care yesterday and they said they had not heard anything about yellow screens and suggested I make appt. with local Genius Bar. Went in for appt. and they said they thought it would be better to just have me return/buy new one through salesperson and said they had not encountered this issue before. Somehow I find this hard to believe. I took my iPad 2 with bright white screen in for comparison. It looked like all the iPads on display. The only yellowish display I saw in the store was mine. I will say that it was harder to see the extent of yellow tinting under the Apple store lighting. Rebought the VZW 64g model. It has a brighter screen but is still much more yellow than my iPad 2 or store models. On this unit, it is the right side or home button end that has the tinting that is observable in the keyboard.
I am running it on full brightness today and will try the towel trick mentioned in another thread tonight to see if it clears up. If i don't see vast improvement in a week, I guess I will return it again and either wait a month or two or try one last time. This has been one big hassle.