Techno-Magic: Augmented Reality in Magic Show

I've found this video on TED and I think it's pretty awesome. It's a video which shows you a show of techno-magic. The augmented reality is implemented in magic show here. Marco Tempest (the guy in the video) says he has some specialty in collaborating the magic and technology. He has done some research on this subject for about 3 years.

However, I'm still curious how the computer renders the color of that man while actually he's standing in the dark.
And how could the sensor detects the canvas (which is held by his hand) that is placed in the dark. It's pretty difficult to detects an object if there's no color difference around it.

However it's a pretty cool video after all :)