Want to add my experience to this thread - it seems like a bug from the update.
My save with an artist who paints almost entirely "paint from reference" paintings have had all of these paintings (in his personal inventory; I'd put none on a wall yet) turn black. They also have turned black in all the rolled-back saves.
All other types of paintings (mostly emotion paintings) and his photos he has taken, are fine. This occurred after I reopened the save after having the game closed for about a day. I did put that "dx11" command in the box after the update.
Was doing a challenge of getting him to paint every single premade before he dies, he'd painted about 24 premades. I guess this challenge is not possible at this time :/