You can also put the viewport in the Monochrome display mode and put selected objects in the Rendered display mode. Then assign an emissive material to those objects:
@wim wouldn’t it be easier to rewrite the Monochrome mode that you can change the color of the background without compromising the objects white color. Would be awesome.
I’m offering things that you can do right now. Like today. Rewriting the display pipelines has been on the list for many years and, AFAIK, is not planned for Rhino 9. If you wish to wait for that, fine…
-wim