I have a lot again. I finally managed to save up some money (your donations helped significantly) and bought a big monitor. It's fantastic and I finally can see some shit since it's relatively huge (27''). When I used it, I understood a few things. 1 - my game is super dark and on a middle range monitor you have to adjust brightness and contrast very high. I found out that my laptop display (yes I used laptop before) just sets very high contrast and brightness by default, so now I understand why some people complained about dark scenes being too dark. 2 - right now I can't adjust brightness and colors for EVERY monitor out there so that they see my game just like I see it.
So I came up with the brilliant idea to add a menu option where you can adjust it YOURSELF HOW YOU LIKE IT. And it fucking WORKS. These options are usual for every decent horror game out there - Resident Evil, Outlast, Dead Space, The Last of Us, SOMA etc. It was kind of tricky but now it is in my game too!