The Witcher 3’s downgrade is a thing. Unfortunately, it has become a very large part of the discourse and discussion surrounding the game. And as is the case with any major game that gets a downgrade to its graphics from its initial reveal (see also: Watch_Dogs, Dark Souls II), an entire modding scene has now arisen, with the sole purpose of trying to make the game look as much as its reveal trailer as possible.
The mods in question are trying to tone down the saturated pastel color base, and trying to increase the sober colors in intensity more- so the browns and the greys are being emphasized. Both of these mods are SweetFX presets, which inject shaders into the game to alter its post-processing.
The first of these mods is is by K-putt, which you can get from here, while the second one is by Powerplay and you can get it from here.