Hi everyone!
For some reason my sprites are too bright.
Here is the screenshot of the material I use with default settings:
This one is with sRGB unchecked:
Generated sprite is identical in both cases:
Does anyone know how to fix this?
You might want to tick the sRGB field 
That should fix your problem.
Diffuse textures always should use sRGB!
Well, sRGB field changes texture, but a sprite using the texture stays the same. Weird enough, the problem was solved by simply “transfering” the file (originally from PS) through GIMP. I have no idea why and how it works
Okay this is indeed weird, but glad you fixed it anyway