Some reflective materials in my project have developed a cast matching a green colour (to which the background was recently set) in any rendered views and in the Rhino Renderer. They did not have that colour cast when the background was set to green, and they didn’t have them before the background was set to green. But now that the backgrounds are set to a neutral colour again, it appears that many if not all of the custom materials I’ve created from scratch for this project which have reflective surfaces have developed a green cast. If I reduce the reflectivity of the materials, the green cast goes away, but if I increase it again, it returns. The reflectivity of the materials remains set to the default colour of white.
(This green cast would never have been an accurate reflection, even when the background was set to that colour.)