How do i exclude niagara particles from a postprocess volume?

Hi i am trying to make this fire retain its colour while everything else remains in greyscale in a postprocess volume. The fire is from a niagara system pack called Perfect Fire VFX, specifically the NS_Fire_Big niagara particle.

here is currently what i have in the postprocess volume

Here are the settings for it

these same settings work for meshes but not niagara particles.

I tried the texture method thing from a previous thread for the texture but this niagara system does not have that setting

Any help is greatly appreciated!!