In response to some questions about computer coloring, here's a tutorial on the method I've been playing around with lately:
1. Draw the most awe-inspiring murder machine imaginable.
2. Scan it into the computer. Even though it's black and white line art, I recommend scanning it as grayscale art, at 600 dpi (dots per inch, y'all). 300 or even 150 will do, but why skimp? Ain't like pixels cost money.
3. Why scan it in as grayscale? As you can see, even a drawing made with thick black ink on clean white paper actually has a lot of other value information. That is, there's a range of grays. I don't want the computer making judgment calls as to which bits of gray are black, and which are white. It'll get most of it right, but it lacks finesse. Instead, I do that by going into Levels (under Image/Adjust in Photoshop), and move the little arrows around until I have exactly the black and white lines I want. This can take well over 6 seconds.
4. To make sure your lines are absolutely Black and White, convert the image to a bitmap. This is a good time to use the eraser tool to clean up any schmutz.
5. Convert the bitmap back to grayscale.
6. Convert the grayscale to RGB.
If these three steps seem like a run-around, let me explain: Bitmaps are files composed solely of black pixels and white pixels. Converting the file to a bitmap eliminates any little gray pixels you might not have spotted. Your lines are now completely crisp, and this will be a big help at a later stage. But you can't do much editing to a bitmap, so we convert it back to grayscale. This, in turn, allows us to convert it to RGB, which gives us the option of adding color. Once you've re-grayscaled you bitmapped line work, try not to drag it around, or resize it, or rotate it or anything, because those gray pixels will sneak back in.
7. Now, go the Layers palette and duplicate the background layer.
8. On the duplicate layer, take the pencil tool, and use a black line to close off any open areas, such as the hair in this image. Anywhere that two colors will meet in the final image should be outlined. Additionally, switch the pencil to white and open up lines that are breaking up areas that will be the same color in the final piece, such as where the eyebrow overlaps the hair.