Okay, new pics and a choice:
I think I like the grey drybrushing (top pic) better in person, but only because it's more obvious -- much like the subtle highlights on Hasbro's most recent Spider-Man Classics Venom figures, the purple drybrushing (bottom pic) doesn't really show up in most light (it's barely visible here, and wasn't really obvious with the flash). That said, whereas the grey drybrushing makes it look like Shredder's wearing grey rather than something darker, I want black to be the dominant color on his body.
So I'm left with a couple of options: simply paint over him in a flat black and be done with it, or paint him some other color (ideally purple, pink, or even blue) and drybrush black
over that. I have no idea how it'd turn out, but I'm going to try it out on an accessory to gauge the effect.
Comments, suggestions, recommendations? Share!