A rainbow is an arch that appears in the sky after it rains. In order for there to be a rainbow, there must be water and light. A rainbow has 7 colors: red, orange, yellow, green, blue, indigo, and violet. A double rainbow is when there are two rainbows in the sky instead of one. The first rainbow occurred after a famous flood involving Noah and his ark in the Bible. Rainbows exist as a promise that there will be no more floods.