Invisible wall


I was wondering if it’s possible to make a wall that affects the render, so if it’s red for example it’ll reflect red onto other objects, but isn’t visible in the render. The best example of this would be the near-facing wall of a Cornell box, where I want it to not obstruct the camera, but still show up in the reflections/bleeding of other objects. I’ve tried using single-sided normals and stuff, but I can’t work it out.