I honestly don't have a GPU in my current box thanks to some IRL shenanigans; even the demo, when it was playable, demanded an embarassingly low resolution; the fact that the art direction and gameplay were still clear is a testament to its strong design!
I do have a hypothesis as to what's happening, though: the game makes frequent use of fullscreen flashes of color, such as when teleporting, picking up ammo and health, etc. I know for certain that the demo starts gameplay with orange flashes; do the commercial version's boot screens start with a pinkish-purple flash? If so, then I think that's the problem there: the effects are not fading as they're supposed to. Is there any way I can try disabling those fullscreen effects from my end?