Guys let me share my experience and disappointment with you. I bought my iPhone 4s on the second day after official release and when they came home and activated the phone I noticed that compared to my iPhone 4 the screen was very yellow. So the next day I took iPhone 4s back to the store Carphone Warehouse, I also took my old iPhone 4 with me to show the difference to salesmen as proof, because I wanted to exchange my IPhone 4s. And the sales guys really tried to make an idiot of me by keeping convincing me that there was no difference between two screens. Then I asked a casual customer to tell us his opinion, he looked at two iPhones and confirmed that there was plain difference in colors. So the sales guys agreed to exchange the phone and said that if a new one appears to be yellow as well I would be able to exchange it at the Apple store. And to my surprise when he came home and activated the phone it was also yellow!! The next day I decided to go directly to Apple store. There before going to the Genius Bar I went around and compared my iPhone 4 with a proper screen with all demo iPhones 4S, and neither of them had yellowish tint!! Not any single phone!! At the genius bar 4 of 5 assistants made big amazed eyes and tried to convince me that the yellow color is white and bla bla bla.. I don't really understand why all of those genius bar nerds never admit a fact of problem existence and instead try cheat on you.. I had some occasion before when I took my MacBook Pro to apple store because my battery was lasting only 2-3 hours instead of claimed 7 hours, and a "genius" guy told me that despite of the indicated 7 hours in the specification description of the laptop a battery never last more than 3-4 hours and always depend on what applications are running.
Back to my iPhone 4s story. The fifth genius assistant fed me with a bullsh*t about an glue issue and that the yellowish tint will go away by itself after some time. But I didn't buy this b*llshit as I had already been aware of the fact that the yellowish tint issue was also encountered on some iPhone 4 phones and my girlfriend had been one of those lucky ones who got iPhone 4 with yellow screen, and after one year of using it remained yellow!!
So after some unsuccessful attempts to convince me the guy agreed to exchange the phone. He gave me a new phone and I left. And guess what, my third iPhone 4S was also with yellow tint!!!! So I gave up and now trying to sell my third iPhone 4S because I cannot put up with a yellow screen. I'm going to use my old iPhone 4 until 5th one releases next year.