I noticed this pretty much straight away on my black iPhone 4S, compared to my iPhone 4 the screen looks washed out and yellow 😟
Really not happy that I am about to sell a phone with a nicer looking screen than my new $1000 AUD one.
This problem is definitely not on ALL iPhone 4S's because I put my sister-in-law's white 4S side by side with mine and it looked much nicer like my iPhone 4. I don't think it's a black v white thing though because I compared it to another white 4S and that also had the yellow tint. Hopefully it is just the glue being too new and it goes away in a couple of weeks otherwise I think I'm going to have to return it. It annoys me every time I use it and see whites looking off-white and blues looking slightly green.
My iPhone 4 was a joy to look at, I was expecting the same experience from the 4S!
Here are some pics
http://dl.dropbox.com/u/7199106/iPhone%204%20and%204S%20Side%20by%20Side.JPG
and it looks even worse on an angle
http://dl.dropbox.com/u/7199106/iPhone%204%20and%204S%20Side%20by%20Side%20angle .JPG