I have a suggestion regarding this. I also noticed a slight yellow tint to my iphone 5 screen in relation to the colour tint of my iphone 4 screen, which was distinctly bluer. After playing around with brightness/auto brightness for a while, I think I may have found a possible solution.
Try setting the brightness to about half way and then activate auto brightness, in a moderately lit room. Then, hold your phone near a very bright light until the auto brightness goes right up to the top. Bring the phone back into a normally lit room, and let the auto brightness come back down again. Now, this may well be entirely phychological, but I tried this and afterwards perceived the screen to be closer to white than it was previously. I wondered if doing this auto brightness process somehow resets the screens colour hue/white balance?
Admittedly, this may be nonsense, but I'm putting the idea out there in case it has some merit. Of course, I may simply have become accustomed to the slightly yellow tint after using the phone for a few hours today. Still, it's worthy of consideration!