I exchanged my two yellow iPhone 4S's a couple of weeks ago. One was from BestBuy and the other was from an AT&T store. Both replacements were new unopened iPhones, but they have the same yellow color cast as the originals. What's more depressing though is both have a dead pixel near the center portion of the screen.
BestBuy will not refund or exchange the one I got from there again, nor anything else ever again for that matter. I was told by the manager that I'm on BestBuy's customer blacklist for returning to much stuff. He even showed me a copy of all the products I've returned. All of them were iMacs, iPads, and iPhones that all had a yellow color cast and/or dead pixels. I tried to explain that to him and I even showed him my phone and compared it to the one on display. It was like talking to a wall though, so I left.
I went to the AT&T store to exchange the one I got from there again, but the salesman said that since it has a dead pixel that would be warranty issue and all Apple related warranty issues must be handled by Apple, even though I bought it from AT&T.
Well, the nearest Apple Store is over a hundred miles away, so mailing them both to Apple would really be my only option. Not wanting to play this game anymore I'm giving them as gifts today, warts and all, and keeping my iPhone 4.
Touché, Apple. Touché.