Digitally colored? Wow. It looks like you used colored pencils for this. Now I'm curious. How were you able to color it without having to digitally lineart the piece? Hope you understand what I'm talking about. Thanks.
I drew and shaded the whole drawing in pencil, then scanned it and duplicated the pencil layer in Paint Shop Pro 9 so that the top layer doubled the black color values in multiply mode. Then each color was added on its own layer (also in multiply mode) and lighting/shadow was enhanced with the Burn and Dodge tools. It's actually pretty simple with the right software and can be done just as well in Photoshop, which is where I cleaned it up before submitting it.