I've encountered this bug a fair amount in my recent testing - but I've never been able to reliably reproduce it in a way that can be contained and sent back to Larian in a save file. If you do find a way to reproduce it reliably, I'd urge you strongly to make a formal bug form report and send them the files. As it is, I think a lot of folks have been seeing it sporadically. It seems to be an issue introduced with the last patch, to do with Vulcan primarily (at least I think it is) - it's lost or otherwise failed to load the correct skin, and that black tone is the default 'base' for the models. The more you see graphical this graphical bug, the more likely it is you're about to have a game crash, I've found... but again, reliable reproduction would be the gold mine here.