Very cool, and almost as good a paintball-waster as the Mythbusters’ “Mona Lisa in 275 milliseconds” demonstration. This one’s a little more controlled, though: you can see more videos here, including one where they’re using multiple colors in layers to create a more nuanced look.
I wonder if they put their “paintings” together in a pixel editor, or just something like Paint. The resolution looks… well, not high. But the dripping effect ends up giving it a unique look for sure. Not that I support graffiti (or can even tell what’s being painted in half the videos). Cool though.