It was a technique pioneered by a painter in the US going by phat bodies (as far as I am aware
), I'm sure there was a tutorial that he did somewhere on it, but a quick search on the net reveals nothing. He used a piece of card held a cm or so away from the body, so that you get a sharp edge then the lower pressure under the card allows some misted paint to 'bleed' underneath it. That's how you create the shape, but as Tel said the layering of various paint colours is truly a work of art.