craftgrrl | Overhaulin on TLC & markers...(?)

So I was watching that TV show on TLC, I think its called Overhaulin'. Anyways, the designer/drafter guy that was designing the new look for the car..the guy that sketches the idea out, and fills it all in with color on paper. Well he was using some kind of markers or something..they were really awesome. It looked like they went on really sheer, and you could layer them (repeat strokes) to make them darker/more vibrant.

I was interested in trying them, but i have no idea what type of markers they are. Can anyone help me out? Tell me what kind they are, where they sell them, how much they run?

I saw some at Michaels, but they had so many different tpyes and varieties..I really didn't know what was for what.