The seven colors of the rainbow are red, orange, yellow, green, blue, indigo and violet. The acronym Roy G. Biv is often employed by teachers in classrooms as a method of helping students remember the colors and their order.
The seven colors of the rainbow represent the layer of visible light emitted by the sun. The longer the wavelength of light and the less bendable it is, the more visible its color. Red, orange, yellow and green have the longest wavelengths and the least flexibility, which is why they're the most commonly identifiable colors in a rainbow. On the other hand, conditions must be extremely precise for violet, the shortest and most bendable of the light waves, to be clearly visible.
Rainbows are optical phenomena that occur when moisture in the air reflects as a prism for reflecting sunlight. Although most people think of rainbows as an arc shape, they are actually circular. From most elevation levels on earth, however, only half of the circle is visible. In extremely high altitudes it is sometimes possible to see the entire circle. Sometimes moisture within the air projects a double reflection. This results in a double rainbow, which is actually two rainbows on top of each other.