I've learned a few things since the first post.

I was incorrect about vsync in fullscreen windowed mode, as learned above (it does actually work). In fact there really is no problem with fullscreen windowed mode; although it does have a very tiny performance hit (negligible maybe 1 frame in 60).

I don't know why it helped other people in another thread switching to fullscreen mode, but perhaps there was some problem in the early versions with the game.

Interestingly though Divinity original sin fake fullscreen can have the framerate uncapped, so perhaps when you don't framecap it just discards the frames if they're not ready?

I had a nightmare with colour management using the Asus ROG Swift monitor. The monitor has no gamma control on it's menu (which idiot thought that was a good idea?), so the only way to set it is using the colour configuration or through the nvidia control panel. But a lot of games just ignore them both :/

Another thing is W2 and 3 both ignore the volume buttons on my G15 keyboard, why?

There is no ingame action for volume adjustment - that is, no other keys for this purpose exist either.
If they existed, a mapping would probably be possible.

I've been suffering from games resetting color profile for years. Until now there is still no good way to solve the problem.

Fortunately, many of the new game engines will not override system's color profile by default. Such as DUNIA Engine(Far Cry 4), FrostBite Engine(BF3), AnvilX Engine(Assassin's creed), they don't mess up player's LUT. Also there are some very annoying game engines, for example CryEngine(criysis), it not only reset the gamma in game, but also reset the color settings of windows.

I thought there would be more and more game developers realize this problem, especially those of 3A games, but I was wrong.

I'm a game programmer by the way. I've written some programs for my own use to hook( inject or proxy) game's process to avoid it to call the gamma function. However, this might be treated as cheat in online games, and it is a very tedious thing to adjust the code for different games. This is really not the way to enjoy the game.

I just hope the game developers to have more respect for the needs of players, and provide more friendly options.

In borderless window mode you can force your profiles with programs like monitor calibration wizard... My profile works that way. In full screen mode the game completely ignores the custom profile and uses windows default...

u guys never heard about sweetFX? maybe it could work for you, here is a link with a profile special made for witcher 3

sfx.thelazy.net/games/preset/3696/

did it work for u guys?

So THIS is why the colors look so bad in Witcher 3 for me? Using a custom Windows color profile and fullscreen mode in the game. Never suspected that the game simply ignored it. Should try windowed borderless next time, maybe it will work out for me :)

I have created a detailed topic about the issue on the official forums.

I have also explained this before but let me remind this again:
SweetFX is not a color correction suite, it is only designed for artistic purposes. Color correction is applied on top of the application(s) as an overlay.

I have also opened up a support ticket for 64-bit applications on Color Clutch's SourceForge hub. But the last time the project updated was 2 years ago. So I do not have much hope.

And lastly, I have posted a reply on Color Sustainer's sister thread on Guru3D. Color Sustainer might have an option to ignore SetGammaControl function in the future.

Again, please do not forget to contact tech support and remind them that you are not happy with the situation.