You've probably seen airplanes of all colors in the sky, but a major of them use white or light-colored paint to give the surface some color. It turns out that the reason behind the use of white paint isn't just cosmetic.
White stays the coolest when exposed to sunlight because it reflects most of the Sun's light away. Unlike dark colors, which absorb some of the Sun's light rays, white helps keep the airplane cooler and protects critical components from tarnishing.
Some companies tried going with no paint at all to save costs further, but they quickly learned that bare metal airplanes oxidize rather quickly, so it meant consistently maintaining the metal surface. In the end, most companies switched to white paint jobs to minimize maintenance.
The same concept is used in a host of school and public transportation buses, where the tops are usually painted white to reduce heat. Of course, when you're so high in the sky, protection from solar radiation is just a little bit more critical than being on the ground.