There are some mods that kill the bright colors supposedly.
Haven't looked into it, and probably won't either - but for those that really feel they want to play in black and white, there's the option at least.
In a nutshell from someone that plays beta and played D2 D1:
- There are some darkish environment, gloomy. Ambiance is very good at creating it.
- There are some gory doodads, bodies on the floor or impaled on a wall. Hanged people.
- The look feels like a dark animation movie, it has a very pastel look to it.
To be honest I very like the graphics, this style fits well and they definitely gave a gloomy/creepy/dark feeling to it, I really apreciate they still made very graphic gory doodads. This is not kitty island, but this is not Dead Space either.