May 19, 2012:
Military aircraft have, like ground troops, long used camouflage to make them more difficult to spot. Sometimes the camouflage is very minimalist. For example, during World War II radar-equipped night fighters were painted black to make it more difficult for bomber crews (the usual prey) from spotting the night fighter soon enough to shoot it down. By the 1980s, the first stealth bomber (the F-117) was also painted black. While the F-117 was largely invisible to radar, it could be seen with the naked eye. Thus it operated mostly at night and was painted black like the older night fighters, for the same reason.
The most recent development is the "digital" patterns found on the infantry and their vehicles, to make aircraft more difficult to spot against vegetation. Air forces use camouflage patterns for two reasons. First, is to make it more difficult for enemy aircraft above, or enemy troops below, from quickly locating the aircraft. For that reason aircraft have two different camouflage patterns. On top of the aircraft is a pattern that makes the aircraft blend in with the ground below (when viewed by an enemy pilot above). On the bottom of the aircraft is no pattern at all but rather a bland monochrome that makes the aircraft harder to pick out from below. The U.S. Air Force has four "looking down" patterns, for different types of terrain. There's even one for the arctic (white, gray, and black). The second use of the patterns is to make it easier to pick out your own sides aircraft. The camouflage doesn't make you invisible, just harder to spot in a hurry.
Not all special paint jobs were to make the aircraft harder to see. During the Cold War some aircraft that specialized in delivering nuclear weapons were painted white, a color that would reflect some of the heat energy from a nuclear weapon.