Roughness for both materials on wall and floor is set to 1.0 yet the wall is still taking on a pink hue from the floor texture too, how do I stop this?
This is bounced light from global illumination. As you noticed, the magenta color is also bouncing off the wall. To get rid of it, disable Lumen/GI. However this will make the lighting less realistic. This behavior is more physically accurate than if it did not bounce, even for rough surfaces.
You can also make the surface less white, so less light reflects off of it. You can also control the strength of the indirect light bounce on a per light basis, although this reduces the accuracy of the light simulation.