We have 2 3GS phones and a 3G
The 3G is perfect. Bright, clear, great colors, no yellow at all.
One 3GS from week 22 -- warm reddish/yellowish tint, sharp, good colors
(the reddish tint is odd, but I like it, so I'm keeping this one)
One 3GS from week 21 -- nicotine yellowish tint, dark, not sharp, washed out colors
We tried to return the week 21 phone to the Santa Monica apple store, but the genius said because we bought it from AT&T we had to return it to AT&T; he said Apple will not replace any phones purchased from AT&T. Only looking at the icons on the black home screen, he said the phone looked just fine and meets Apple's specifications. We didn't bother arguing with him, the guy was not going to help us.
We called AT&T and they said that's not true, Apple handles all returns. AT&T transferred the call to Apple, and Apple sure enough Apple replaced the phone, even though this phone was one ordered on-line at AT&T and shipped by AT&T originally.
The new one arrived by FedEx today. It's a week 25.
It had interesting packaging. There were two boxes side by side in foam in the package, each box is half the thickness of a regular iphone box and slightly larger. One was black and said "iphone" in silver and the other was white and said "AppleCare" in red. The new phone with no accessories was in the iphone box, and the white box (which to me looks like a little ambulance) contained a little bubble-wrap envelope to place the "broken" nicotine-yellow iphone in so it could go on a safe little ride back home to the Apple hospital.
I assume these replacement units are new; but they are in their own unique packaging.
This new week 25 3GS does not have a nicotine yellow tint, it is sharp, and the colors are well saturated. The chrome is flush with the screen. I notice an ever-so-slight yellowish towards the bottom of the screen, but it's not that bothersome. We're keeping this one.