It's not always heat related. As I said before in my case its CPU and auto-brightness related. There is a very specific range of brightness where I get flicker ONLY when the CPU usage is high such as rendering a web page. It stops flickering once the page has finished rendering. Dimmer brightness, no flicker. Brighter, no flicker. Just a specific range, and in addition, the same brightness level with auto-brightness disabled doesn't give flicker.
I would bet that nearly every phone has flicker under specific circumstances. But due to tolerances, each phone will vary slightly on what induces it. I believe this is hardware and related to voltage regulation of the backlight. I would be surprised if there was a cure for this in firmware unfortunately. I think its a bad choice of component for the backlight voltage regulator.
EDIT: I have seen both phones with the whiter screen and the more yellow variant flicker. The voltage regulator for the backlight is not part of the screen itself.