Hey Ayan, may you be more specific on how the material is set please? 
If you solved the problem it would be just amazing, I got stuck so bad on it.
This is post-process material setup. Just a color and blending mode:
This is screenshot from the editor viewport:
Edit: updated screenshot of material to correct one. it should be After-Tonemapping.
Replacing tonemapper seems to work better. This is “Replacing Tonemapper” mode and bunch of cubes with unlit material in the scene. PP material is just SceneTexture:PostProcessInput0:
It actually works! It kinda fu*** up all the colors and stuff, but all you need to do is to tweak few mats from scratch. Thank you so much, I was completely blocked!