Miscellaneous bits of black
A few random points, relevant to some of the earlier comments:
Current stealth technology depends mainly on the geometry of the aircraft: the surfaces are so angled that hardly any of them reflect back any part of a radar beam. Hence the weird non-aerodynamic shape of stealth fighters and bombers, and the need to have a computer to fly them, since they won't glide.
The radar signature of the average stealth aircraft is the size of an eagle's eye, not the whole eagle (a selling point strongly pushed by the Lockheed Skunkworks during development).
Lockheed nicked the basic idea from a technical paper published by a Soviet scientist who did the maths back in the 1950s (or early on, anyway) before computers were adequate to the job of keeping such a thing airborne.
If you change the geometry, you lose your invisibility. During the first Gulf War, a stealth pilot reported that his bomb bay jammed open, whereupon he was lit up like a Christmas tree and saw a radar-guided missile homing in on him. Fortunately, his bomb bay doors unjammed in the nick of time, and the missile careered off (muttering "Where'd he go?", presumably). Ultra-black paint would avoid the geometry problem, but you would then be faced with keeping it clean, since muck would clog the pores on the paint and make it reflective.
Regarding seeing a non-reflective object as a hole in the background: that is why stealth ships were not developed. The concept was tried, but there is significant radar reflection from waves at sea, and a stealth ship shows up nicely as a ship-shaped black hole in the radar background.
Furry cars were tried back in the 1970s (not sure of the precise date). The intention was novelty, not invisibility. They were covered with a special paint that used electrostatic charge to raise "hairs" on the surface after being sprayed on, giving a matt finish. The effect was disappointing. A car body is designed so that it reflects attractive highlights. Remove the reflection, and the result is just dull. Add to that the fact that the "hairs" wore off in patches. I saw one once, and it looked like a mangy beetle. (In fact, it was a Beetle.) Furry cars were a seven-day wonder. So much for civilian artistic uses.
Whoever said it would be good for the anarchist flag is forgetting that said flag is black and red. If you want pure black flags or shirts, join a slightly different party.
Paris Hilton since she looks better sprayed gold than matt black all over.