Fading True Tone on iPhone 13 Pro Max / iOS 16
There seems to be a bug in True Tone at least on iPhone 13 Pro Max and iPhone 13 Mini on iOS 16. - In darker environments with warm light the display starts out with a noticeable yellow hue but over a minute or so the yellow hue gradually fades until True Tone almost stops having any effect.
After you turn the display off and on again the display is back to yellow but just to fade once again.
You can prompt the bug by turning True Tone off and on. After turning True Tone on again, the display of the affected device stays white despite the warm environment.
However, iPhone 11 Pro Max on iOS 16 seems to handle it correctly. It stays yellow and it also returns to yellow even after turning True Tone off and on again.
The attached comparison video shows the iPhone 13 Pro Max to the left (eventually turning white) and the iPhone 11 Pro Max to the right (eventually staying yellow).
The iPhone 13 Mini seems to have the same bug.
iPhone 13 Pro Max