Always remember, ROY G BIV.
When you see a rainbow, it is actually part of the electromagnetic spectrum known as visible light. This part of the spectrum can be detected by the human eye and falls between 390-750nm in terms of wavelength. When sunlight passes through water droplets in the atmosphere, they can act like a prism and separate the white light into the colors of the rainbow. These colors are red, orange, yellow, green, blue, indigo and violet. Red waves are longer and violet are shorter. You will see the color red on the outside arc of the rainbow and the violet on the inside arc. You can remember the visible spectrum by memorizing the name ROY. G. BIV. Each letter in the name corresponds to the colors of the rainbow. R stands for red, O for orange, Y for yellow and so on.
A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines on to droplets of moisture in the Earth's atmosphere. It takes the form of a single arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun.
In every rainbow, there are seven separate colors. Although it can be difficult to always see all seven colors (depending on the conditions outdoors when the rainbow appears), every rainbow contains the following colors: red, orange, yellow, green, blue, indigo and violet. Because this is the spectrum of colors that every rainbow spans, it can be useful to come up with a way to remember these colors. Fortunately, there is a mnemonic device that makes it simple to remember all seven colors that are in the rainbow. The mnemonic device that will help you remember these colors is “Roy G. Biv.”