Rainbow

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 multicoloured arc, with red on the outer part of the arc and violet on the inner section.

A rainbow spans a continuous spectrum of colours; the distinct bands are an artifact of human colour vision. The most commonly cited and remembered sequence, in English, is Newton's sevenfold red, orange, yellow, green, blue, indigo and violet. Rainbows can be caused by other forms of water than rain, including mist, spray, and dew

Source: Wikipedia