I wonder if the yellow tint issue could be resolved with a software patch?
I got a 4s about a month ago with a distinctive and rather unappealing yellow tint.
I installed a Cydia tweak called ColorProfiles and was able to adjust the screen colour temperature to match that of my iPhone 4.
I'm not quite sure what Apple is playing at with this yellow tint issue but it is to their detriment with the majority of users preferring the blue, white tint of older models
I remember reading about the yellow tint issue. Wasn't it caused by the bonding agent not finishing drying for the first week of production devices? And went away after a couple of days