The colors of the rainbow, in order, are red, orange, yellow, green, blue, indigo, and violet. This sequence of colors forms a spectrum of light that can be seen when sunlight is refracted, or bent, in raindrops in the sky. Each color corresponds to a different wavelength of light, with red having the longest wavelength and violet the shortest.
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The phenomenon of a rainbow occurs when sunlight is refracted, or bent, as it enters a raindrop, then reflects off the inside surface of the drop, and finally exits the drop. This process causes the light to spread out into its component colors, creating the spectrum we see as a rainbow.
Each color in the rainbow corresponds to a different wavelength of light. Red has the longest wavelength, around 700 nanometers, while violet has the shortest, around 400 nanometers. The other colors of the rainbow fall between these two extremes, with orange, yellow, green, blue, and indigo in that order.
Interestingly, the concept of indigo as a separate color in the rainbow is somewhat arbitrary and not consistently observed by everyone. Some people consider the rainbow to have only six colors, excluding indigo and combining it with blue. The decision to include indigo was made by Sir Isaac Newton, who believed that the number of colors in the spectrum should match the number of musical notes and planets, both of which were considered to be seven at the time.
Rainbows are not limited to rain showers but can also be seen in mist, spray, and dew. Double rainbows, where a second, fainter rainbow appears outside the primary one, occur when light undergoes two internal reflections inside the raindrop before exiting. Double rainbows have the color order reversed in the outer rainbow, with red on the inside and violet on the outside.