Lowering the saturation of the view

So, i am making a horror map, and i want it to have less saturation.
I know i can use a env_screenoverlay used with “debug/yuv” or whatever to make it black and white.
But is there a way to make it only take out 50-75% of the saturation?

Colour correction perhaps.

Ah yes.
good point.
Ill check that out