As posted some years ago it seems impossible to use decals with Rhino 6 on my laptop with Windows 10 and Intel grahics.
The view then was the bad quality of the Intel graphics caused the problem, but I have found that by creating a custom material for a surface and choosing an image as texture gave the same result as the decals function.
It seems Rhino 6 decals is not working well with Intel graphics and not the other way around!
Can this be remedied?