Looks like the environment map (rhino_shaded_mode_emap_background.png) used for the Shaded view was swapped with another one that produces that rainbow-like texture. It would be easier for those who have the issue described in this topic to simply replace the wrong environment map with the proper one. Its folder is C:\Program Files\Rhino 7\System
Alternatively, as a temporary solution, they could make a custom viewport mode that uses the exact same settings like the default Shaded view and set the same environment map stored in some folder of their liking. Not the best solution, but still could help until an official fix is published. This one has some custom settings done by me, but they could be changed by you according to your liking:
Shaded 2.ini (13.9 KB)
I also posted it here: