I’ve noticed that on some devices the colours of my game look wrong. Some android devices they look okay, but some players report them looking too washed out and bright.
I’ve attached examples.
Keep in mind the players have different darkness levels, but you can see the washed out image almost looks like it has a grey filter washing out the whole image.
Lack of SRGB backbuffer support would have been my first guess but you said, you are using gamma color space.
Samsung phones allow you to change screen mode (e.g. Adaptive display, AMOLED cinema, AMOLED photo, Basic) and white balance but this might only be for the display (you took a screenshot, not a photo of the display). Obviously, all phones allow you to change brightness. Neither seems very likely.
Maybe it has something to do with low precision floats in shaders (lowp, mediump, highp)? Are there mobile devices that don’t support low-precision floats?
Struggling to come up with a good idea too but maybe it would help if you could told us what devices/gpus have that problem.