Last year there was a ton of controversy about yellowing of the displays and the colors being too warm. Apple must have listened to feedback because I just got my iPhone 13 Pro and I can confirm it doesn't have this problem. I tried the iPhone 12/12 Pro last year and it was always way warmer than my iPhone X. In comparison to the X, the iPhone 13 Pro is actually cooler this time around, but not too much so. This is with true tone enabled on every device. Apple must have done some calibrations or adjusted true tone because it's a big difference.