In my incessant quest to find quicker ways to paint miniatures, I've been trying Citadel's contrast paints over a black undercoat. After undercoating in black gesso, I drybrush in grey and white before slopping on a coat of contrast. I think it works fairly well. In the case of the beastie above and below, I painted the bone and belly-scale areas buff before the white drybrush.
With these crab-men or selenites or whatever they are, I drybrushed silver-grey over base-coat colours (red and buff) before adding the contrast.
These leeches were straight black/grey/white contrast:
So was this fishy thing:
And these space orcs - very quickly done for friends' children - were my first experiment. Black/grey/white/contrast again; it took just an hour to finish all three:
They may be crude (and it's not a great photo), but I quite like the effect. I'm painting up another batch for domestic use. Here are how they look along the way:
And here's a Reaper Bones troll who's there or therabouts with the same technique:
It's never going to be a prize-winning technique. But for quick monsters, it's actually quicker than using contrast paints over white, because the black undercoat takes care of the joins and recesses. So there's much less tidying up to be done at the end.