In total candor, I found the original monotone state of this drawing a bit flat, though totally beautifully drawn. To me it cried out for some sort of tonal values to give it a bit of depth. So, I gave it a duotone treatment. And if you don't like that, for you purists I've included the original state below that.
This is a total side note, but it's an autobiographical blog, so I'm entitled. Before I was married, I dated a couple of young women, who as I got to know them more, revealed that they liked to color with crayons in coloring books, just for mindless relaxation. I found that to be charming and endearing and I never discouraged those sorts of 'hobbies', even though I had no desire to emulate.
Until now. With digital programs I find myself taking existing line art and having at it with colorizing techniques. I can justify that, I tell myself, thinking that I'm training myself to be a colorist for the comics industry, but in reality it is mindless relaxation.