Yes, as Hickory says, the game (and The Witcher 1, based on the same engine) looks like it directly modifies Windows scheme, and also, desktop gamma. So it just throws off the colors / brightness (both linked). However if your scheme isn't restored properly even after doing a full shutdown of your PC (all OFF, 30sec wait or so) and/or resetting driver color settings and monitor's (shouldn't have changed, but eh) to default, it gets more complicated. If you're using pre-Windows 10 OS, try 'disable Desktop Aero' in the compatibility settings (right-click on game shortcut > Proprieties > Compatibility).
If nothing works, well you may have a bigger problem, not with brightness alone, but with color profile management, and I know the game can directly alter your desktop color profile, as I've done some tests about that some time ago.
Now that I think of it, you could try window mode (howto:
http://pcgamingwiki.com/wiki/Neverwinter_Nights#Windowed ). I'm not sure at all it will solve anything, given the game is one of the few that allows for brightness/gamma change even windowed. (otherwise, windowed mode is a simple way to retain your color profile while playing in many cases).
To check if this isn't an issue related to color profiles then, open your 'Color Profile Management' window (type this in in your Search bar in Windows, it should show up).
Then look at the list of profile(s) linked to your monitor, check if there are more than one. If you have never created (or installed) another color profile, you should only get one there, your default (= monitor's factory settings). To double check, tick the 'Use my settings for this device' at the top (the drop-down list right above should have selected your monitor + GPU by default).
So, it may show other profiles - not a good sign if you never played with that before. Now, a good idea would be to go back to the basic profile. To do this, ensure you have ticked 'Use my settings for this device'. 'Set this profile as default' should become available in the bottom right corner (or something like that - my OS is in French). Click on the profile at the bottom of the list (or even if there's only one, click on it!), there's a good chance it has a simpler name than the others (maybe even the same name as your monitor, or just 'Windows something'). This should be your factory, default, original color profile. Now, 'set it as default'. If all this has any relevance to your problem, your should see a shift in color/brightness on your Desktop (ranging from subtle to utterly terrifying - or cool!).
Although this means you will need to 'lock' this profile (or any profile of your preference) when the game is running. Let's just see what you find first!
