What's an easy way to do this? I can't do it by hand. Maybe a really thin black wash?

if you're talking about coloring panel lines. then the easiest cheapest route is a Rapidoliner pen. Cheap kind are would be those Micron fine line pens you find in an arts/crafts shop.

Hmm, I'll look around for those. Thanks.

A thinned model paint will work too. Check Jin's custom guide for a link to his site that talks about it. Or use a pen, but it sounds like you don't want to do it by hand.

I do blacklining by hand, it turns out nicer that way I feel. Just snag a really tiny brush (I like the Kustom Kolor series at Wal Mart because they're cheap and last about 2 months without fraying) and mix your paint up in a ratio so it's a tad thicker than a wash. Say 3 parts paint, one part water. My technique is not to take so much time staying in the lines, but wiping the surface gently with my thumb to remove any over-spill from the panel lines. It's cheating, I know, hehe.

You can either do as Jin says, and paint the panel lines in by hand, or rely on your surface preparation. For example, a common start is painting the figure completely black. You can then paint the outer panels, and not touch the cracks at all. If you accidently get paint into the lines, just use a brush and fill the line with black again. You have options, and using all of them at once ain't bad.

They make something called a "Gundam marker" specifically for filling in the lines on models and the like. I got one at a local comics/hobby shop a ways back.