I gave it a try to make saturation shader. It is literally just that: changing saturation. If *that* is really wanted for more "realism" is to be decided.
(also i have no idea of HLSL so it is probally horrible)

1. Make backup of original file
   
2. Use the file in attachment to replace the file in folder LFS\data\shaders
   
3. Enable post-processing in options
   

In this line it is possible to change the factor of saturation:

Quote :

float factor = 0.2f;

1 means normal
0 means greyscale, no colors at all.
Any number inbetween results in something inbetween. (oho)
For reference: I think the formula picture was 0.2 and the other one with 0.5

This replaces LFS's original post-processing formula, to use both is possible but I was lazy.