Had an F18 serial iPhone 12 which was really yellow and had severe colour shift on the vertical. started giving me eye strain. Went to the apple store and checked against 3 iPhone 12s and 3 iPhone 12 pros and all looked the same - minus the brightness on the regular 12s. Exchanged through the carrier and switched to an F17 serial and it's much better, still very slightly yellow but thankfully no colour shift at all which I can get used to. TT was way to yellow to use on either phones. I'm in the UK btw. My ipad air 3 display still seems perfectly calibrated compared to all the the iPhones I saw so far.