"It's some sort of treatment, apparently." So that's a yes. "Strange wanted to try it, and I foolishly agreed."

He rubs his face with a groan, stalling before he shifts to sit up and look back at Childermass. "I did not know it was going to... soak into my skin like this."

It's not a problem for most races, whose flesh is not porous enough to actually absorb dyes like, well, plants do. And he's a very pale plant.