Excluding Color From Post Processing ?

Hey this is my first time posting on the forums, hopefully this is the correct area for my issue.

Currently I am working on a level for my course, and I wanted to go with a Sin City style of game. ( Black and white with certain colors such as Red, Blue, and Yellow that are still visible in game.

I achieved the Black and white by using a post processing volume and tuning off the saturation ( however I found no way to exclude certain colors, objects or materials from this. (
I have played about with the film tint settings by turning up the red section ( however this just makes red objects generate light (

My tutor told me that in UDK (unreal 3) it was possible to exclude objects taking light. However after searching we failed to find anything.

Any other methods to achieve what I am after or is the process not possible yet?

Thank you.

Rather than do it in post, you can do it on a per-material basis.

Ideally, I’d do this in post, but I feel that the best way to do this would require a 24-bit buffer that can be drawn into in the same manner as other scene textures (e.g. diffuse), but this feature is not available in UE4 unless you want to add it yourself.

You can also achieve this with a color lookup table but the same LUT wont work for every lighting condition, since you can mask out colors but highlights and shadows may be problematic. You can see an example here and download the lut collection here.