Sketch of the Week: Coloring Book Skull

As a lot of readers probably know by now, several months ago I published a coloring book via CreateSpace, Clever Animals. One is never enough, however, and at the suggestion of a friend, I've been considering making a second book with a skull theme. The other night then, I took one of my old sketches and reinterpreted it with a zentangle aesthetic. Obviously I'd used a finer pen in the final coloring book version, but I think it has potential:

How would you like to color this?