I haven’t seen this. Can you post the 3dm or send it into tech@mcneel.com? A screenshot of your OpenGL info from Options>View>OpenGL would be good to see as well.
I’ve discovered that if you explode the polysurface and join the surfaces individually, it behaves correctly. If you explode that, then pre-select and join, the colour problem reappears.
Hi Dan, I see that here - thanks. Hm - I see a tiny sliver surface on the end - that seems to be the culprit. There are 6 real surfaces, which work right, then adding the sliver in sends it all south. It seems only to be selectable by selecting the six real surfaces and then Invert. That should be a bad object, I’d think.