Maybe it's the prison reference, idk, but a book of tattoo designs jumped into my mind... they'd have good lines for different dark/light shading to make an impact. I don't remember any offhand, but I know I've seen some on here, so maybe an Amazon search for tattoo colouring books.
[edit] I found this one ... with some gold detail filled in, it might lift the images a bit. UK search, though, maybe look for something similar if you can't get that one. There are a few colouring books out there with details filled in with silver or gold effect.