Many iPhone 4S users are complaining their screens have a yellow tint. The newest launch defect has been dubbed Yellowgate on the Mac support forums.

Here is how one user described the problem on Apple's forums:
My 4S screen is less contrasty, and the whites are more yellow (beyond warm) compared to my iPhone 4 screen. The colors are less vibrant, and some are pretty washed out. I've also noticed that the screen is more directional than the 4 screen, and in some viewing angles it's more yellow, and in others it's more contrasty. I'm really hoping this is a glue issue, which could improve. I don't think I'll be able to get used to this.

Apple users have noticed a yellowish tint on their products before. Yellow blotches have been attributed to the glue that was used to hold the screen to the rest of the body not drying or being properly cured. However, those issues went away in about a week after the glue was given time to dry.

The problem may not be due to wet glue. iPhone 3G owners have seen this yellow tint too. One researcher claimed the problem was caused by certain cases blocking the light sensor. Also, the iPhone 4S's entire screen has a yellow tint. If it was a glue problem the effect would be more pronounced around the edges. And the glue wouldn't account for the washed out tones of the new screen.

A review of the iPhone 4S also saw the yellow-tint and described it:
One thing I did note, however, was how much less contrast-heavy the screen looks in comparison to the previous model. The iPhone 4S has a noticeably different color tone, and blacks seem far less dark, Reviewer Joshua Topolsky said. ...side-by-side, I found the iPhone 4S display more eye-pleasing. Still, the newer screen definitely has a slightly more green-tinted, washed-out look compared with the older device.

The issues seem to occur more on the black iPhone 4Ses but owners of the white model have also complained.

New gadgets often have a few kinks to work out in the first few weeks after they launch. The iPhone 4's biggest flaw was an antenna that was easily blocked by users' fingers. This would cause the iPhone to drop calls in callers held their phones wrong. Apple fixed the problem by offering free cases that would prevent fingers from blocking the antenna.

In the past, Apple has offered to replace most defective products. Many users have said they will wait two week to see if the problem resolves itself and then will go to the Apple Store if the yellow tint persists. Other iPhones have been reported looking fine, so the problem isn't ubiquitous.

Apple has yet to comment on the yellow-tint problem but we'll keep an eye on Yellowgate as the story develops.