Posted this over on the Apple Discussion on the yellow tint
https://discussions.apple.com/message/16969710#16969710
Back from my trip to the Apple Store Genius bar. Firstly going at 17:10 on the 2nd Saturday in December is a BAD idea, dear me was that place busy.
I checked in and was immediately deflected being told that Apple Support (who told me that I SHOULD go to the store and get it exchanged as it was obviously wrong and a known issue) "shouldn't have told you that it can be swapped, we don't exchange for yellow screens.". I pointed out that I understand that might be the case but I'm sorry that was not what I was told by Apple Support, after persisting he said would go speak with his manager and after a couple more minutes returned and escorted me to an empty table and told me to wait.
After 10 minutes a Genius tech came over, asked to see the phone and I showed him side by side with my wifes 4 and he agreed that there was a difference and that this time they would exchange it. Thankfully I got a chance to compare all three side by side (4, new 4S, old 4S) and the screen was much better than the previous 4S.
The screen isn't "perfect", it is still a little yellower than the iPhone 4 and blues aren't as blue (like nav bar in settings or Safari) however but it doesn't have the washed out look of my original 4S and at full brightness is much brighter (in a good way) than the 4. Indeed off angle viewing is MUCH better compared to the 4, on the 4 it goes a muddier dark colour. I do think the contrast isn't quite there, certainly on the App name text. Some colours look better on the 4S and some on the 4.
So, so far, its better than the previous 4S and better in some ways than the 4 and not quite as good in others. No idea how the rest of the phone stacks up, I am in the progress of restoring it now