Hey leitch,
I do a couple of things along these lines (forgive the pun) for overall black aircraft.
I'll sometimes use some brown tones (pastels) as well as grays, but I've actually found black pastel to be very effective. The black of the pastel and the black of the paint will invariably be different, the pastel will appear to be a bit lighter. I also buff the panels a bit just to suggest some variation of sheen. And when using pastels, I usually will work on the panels themselves, leaving the lines dark.
I generally don't do too awful much on a black aircraft, it's easy to overdo things. Here's some photos of a Hurri that I did some time back:
Fade to Black...