I attach some pictures that show the change of colour temperature when in lockscreen.
Maybe this helps to identify software bugs related to screen…
What i also saw a few times is some kind of a brightness flash, like the brightness of the screen flashes to maximum and regulates down to normal within a second or so. Happens randomly. Saw it on both phones.
On FP1 with Beta version of FP2’s OS this was called “Mood Background” and could be deactivated in Settings > Display, but that setting is missing on the FP2. Strange.
I changed the wallpaper into a greyscale one, but the lock screen now shows it with a yellowish overlay. Is there any way to change to colour of this overlay?
This yellowish color is just an indicator that your battery is getting low. The lock screen changes its color according to how full your battery is. Unfortunately, I don’t remember if and how the feature can be switched off.