(no subject)
green "chromakey" paint, or "greenscreen" is used when you are going to composite, or "comp", a live image onto an already captured one; the movie 300, or Amanda Tapping's series Sanctuary, for example, are projects almost entirely done with greenscreen.
the actors and small bits of real sets - along with any props needed - are shot in front of a green screen, and then when the background images get created the two sets of images are merged into one. "bluescreen" is exactly like greenscreen only with blue chromakey paint. blue is used if whatever you are shooting live has large amounts of green in it.
for something like what this project was, or live news/sports broadcasts, the compositing is done live.