Quote - "*I don't know how to attach a Rainbow like color map to the highlights channel. I'm not sure if that can be done in the basic material editor or if I would need the FE.  But if I could figure out how to do that in the basic material editor, I could then probably handle adding an angle of incidence node in the FE.*"

Yes, it must be in the FE. See the image, I hope it becomes clear. You can use other color maps, of course, this is just one of the Vue default ones (it's in Terrain editor maps, it's called "engineer").