I also just had a bad experience with Apple and their pee colored displays - then happened to stumble upon this thread.
I contemplated for a week whether it was worth shelling out the cash to upgrade to a 3GS model from my perfectly fine 3G. I took the plunge - I found a store that still had stock, drove an hour away, stood in line, and paid $560 to upgrade.
The display had an obvious yellow tint compared to my 3G and even my fathers new 3GS, which he purchased 2 days before I did. My phone's display was lower quality in terms of color (and detail if comparing pictures). I spoke with an Apple tech on the phone who walked me through rebooting and restoring the phone to factory settings, which neither made a difference. I then made an appointment with the Genius bar over at the store in Pasadena, CA.
The "Genius" tried to explain to me that this was a gamma change done intentionally by Apple in the new 3.0 software. I showed him the difference on my 3G phone, which also had the 3.0 software loaded onto it.
He then changed his explanation and said it was only done to 3GS models. I explained that my father had also bought a new 3GS model and didn't have this problem, and he said the display should look like my 3GS.
I asked him why would Apple lower they quality of their displays from the 3G models. He said they are not lower quality, it's because the 3GS models come with new screens.
I argued and ask him to explain why my 3GS is different than my fathers. He told me that Apple gets their screens from different manufacturers, and there might be differences between units.
I told him that if I'm paying $500 for a phone, I want a guarantee that I will get a good screen. He told me, "Oh well, get used to it or return it".
So I did just that, returned it. I'm very unhappy with the way Apple handled my situation, and the "Genius" was a ****** bag. My phone was from week 25 BTW.