Thanks for the suggestions. My project, with a working title of "Making an abused PowerBook look cool," is more or less complete.
Since I didn't want to buy an entire can of spray paint for one square inch, I scrounged up a dark blue piece of plastic that fit nicely in there, so it's blue now. I'll link to pictures of the whole thing when I get them.
If I find something else that could use up the bulk of a can of paint, I'll probably go ahead and paint it black.
Unfortunately, I couldn't really change the bottom logo (I was just going to pull off the plastic logo to expose the black plastic below, but there's a screw stud underneath the apple), so it's black, silver, and white on the bottom. Maybe if I find a thin sheet of glossy black plastic I can change it out.
For now, it looks pretty neat... for a weekend experimental project. If anybody is interested, I can write up a how-to for this.