How would I make a green screen that has absolutely 0% reflection, and does not cast or receive shadows? I tried making a plane and making a material and changing the background color, but every time there would be a reflection on the objects in the scene.
This is what the Holdout shader is for:
This shader affects the alpha channel when Transparent is enabled in Render settings > film.
If you really want to create an actual "greenscreen", then see Node for setting render colour, regardless of lighting