I based the settings on my monitor's colour and brightness values so this may appear too bright or too washed out for your monitor (See lower down for suggestions for alterations)
For me, at least, this makes the day time more natural looking and moon lit nights look very good (IMO). Stormy weather doesn't look as dark, and Inns don't as gloomy.
If you find the settings too bright, or under saturated for your liking you can tweak these settings a bit
#define TechniPower 3.40 (perhaps change it too 6.00)
Or
#define Technicolor2_Brightness 1.5 (perhaps lower this to 1.0)
To give it more colour
#define Vibrance -0.28 ( lower this to maybe -0.10)
To use:
To use copy the SweetfFX_settings.txt to your sweetfx folder, if this is where its located, or it maybe where the game.exe is. This seems to be depedent on if you used SweetFX, or reshade & Sweetfx2.0
Mine is in : Steam\steamapps\common\The Witcher 3\bin\x64\SweetFX.
NOTE: Please backup your current SweetFX_settings.txt file before you copy mine over, as I don't have an original anymore.
Credit to the Creator of Sweetfx; CeeJay.dk