I followed the yellow screen threads for months now and this is my summary:
-All iPhone 5 have warm, yellowish displays. It stands out against blue-ish displays (iPhone4, iPad 1 f.e.).
-The tone differs between phones, but it is always on the warm side (again against the blue-ish displays)
-The iPod Touch 5G also has has the same display.
-The iPad 4 also has a similar color tone.
-All new yellow displays have more vibrant, deeper colors than the old blue-ish displays.
This is my conclusion:
-To achieve the vibrant deep colors, all new displays seem to share the yellowish whites as a trade-off.
-You won’t find a perfectly white iPhone 5, iPad 4, only variations of the warm tone.
-I reported the issue directly to an Apple engineer, so Apple is aware of the »effect«.
-I checked approx. 50 iPhone 5, you may only get slightly different warm screens, never blue/white.