How to render OnPostRender with other custom post process render filters.

I made a script attached to camera that renders some extra transparent geometry shadow vfx in onPostRender() this works fine.

However, I'm also trying to use some post process filters from 'Colorful' asset store shader pack. CC_fastVignett and CC_Vintage They both use use OnRenderImage and Graphics.Blit but if either of these 2 filters are enabled... Then my code renders nothing. does anyone know why ? or how to change things so I can render both my fx, and also use the Colorful shader filters please. Help appreciated, thanks !