My first 3G S had signal issues so I swapped it out through the ATT store. My second phone - the one I have now - is horrible as far as the yellow goes. I went back today to check some things out. They have a 16 GB 3G S on display and when I compared mine with that, it was night and day. Mine was dingy and basically - piss yellow. It was blurry, washed out and looked like crap. The display one was crisp, white, even brighter (both were at max brightness). Colors were superb as well. I asked to see my old 3G S and it was better, but not by much.
There should not be that much variation on screen color out of the box. I will be taking mine back to the store and will go buy a new phone at the Apple store. I might wait a bit and see if they get new stock in or something. I will not be stuck with a phone that looks like crap.
I honestly wish I had my 3G back. It was beautiful, white and crisp. Hell, I didn't even know about this yellow issue during the 3G launch. My phone just looked really pale and yellow and decided to do some searching. Glad I was not the only one.