Here's a little something for fun! A Manga Software developer has created an automatic coloring tool for your browser that fills in your line drawings. Read more about it here. You still have to set some parameters, and it may not get you precisely what you're looking for, but many people have been ending up with something decent! Have any line drawings lying around? Give the software a go and see what you think! Or check out the scrolling twitter images on the right of the link for samples of other people's results!