The colors seen in a rainbow are light refracted in water droplets, such as rain or a fine mist, reflected back and then refracted again. Refraction of light is the bending of a light wave where it enters a medium, such as water or glass, where the speed at which the light can travel is different. When light is refracted, the different colors in the spectrum are separated.
A rainbow is formed when there is a good amount of sunlight and rain or mist, often seen at waterfalls. To see a rainbow, the person must be facing away from the sun, looking toward the precipitation. When the light reflects within the droplet of water, there is a chance that it will reflect again, causing a double rainbow or a supernumerary rainbow. A supernumerary rainbow occurs when additional bands of color form on the inner, and rarely the outer, arc of the rainbow.
It is possible to recreate the refraction of light seen in rainbows by using a glass prism. The number of colors seen in refracted light can be as many as 100, however, due to the sheer number of variables in forming a rainbow, the number of colors visible can change greatly. The seven colors associated with rainbows-red, orange, yellow, green, blue. indigo and violet, can be traced back to Isaac Newton, which he associated with the seven notes in a musical scale.