For the British hard rock band, see Rainbow (the band).
A rainbow is an arc of colors in the sky visible when the sun shines through falling rain. The colors, known as the spectrum, start with red on the outside and progress through orange, yellow, green, blue, indigo, and violet on the inside. Sometimes people see a second rainbow that is larger and darker.

Rainbow during the Tolbachik eruption 1975-76:
Kamchatka Krai, Russia

Rainbow near the blooming Nashi pear tree
Rainbows are created when white light is bent (refracted) as it enters drops of water, separating into drops of color and reflection. A rainbow is really round like a circle. On the ground, the lower part is obscured, but in the sky, such as from an airplane in flight, it can be seen as a circle around the point facing the Sun.
Rainbows often appear after storms and are a popular symbol of peace in many cultures.

Cause:
A rainbow effect can be seen when there are water droplets in the air and the sun shines its light behind the viewer at a distance or low angle. Rainbows always appear to face the Sun:
they form circles around the shadow of your head (which is the point facing the Sun).

While sunlight is white, all white light is actually a mixture of several different colors. Water and other materials bend different colors at different angles, some stronger than others. This is called dispersion. By separating white light into separate colors, rainbows appear colorful even when the light source hitting them is white.

Rainbows show with the deepest effect in our minds when:

Half the sky is still dark with flowing clouds; and
The Observer is in a position with clear skies overhead.
Another popular place to see the rainbow effect is near waterfalls. Parts of the rainbow can sometimes be seen:

at the edge of a backlit cloud; or
is the vertical spectrum in distant rain even though it does not fall over land.
Unnatural rainbow effects can also be created by spraying water droplets in the air on a sunny day

Seven colors of the rainbow
Rainbow -sky has no fixed number of physical colors specified, but the seven colors are traditionally listed. Below is a list of seven commonly used colors in the order seen in the rainbow. Computer monitors cannot display them correctly

Red (Hex) (RGB:
255, 0, 0)
Orange (Orange Color Wheel) (RGB:
255, 127, 0)
Yellow (Net Color) (RGB:
255, 255, 0)
Green (X11) (Electric Green) (HTML/CSS "Lime") (Color Wheel Green) (RGB:
0, 255, 0 )
Blue (Net Color) (RGB:
0, 0, 255)
Indigo (RGB:
46, 43 , 95)
Violet (Electric Violet) (RGB:
139, 0, 255)