A rainbow is a natural phenomenon that displays a spectrum of colors in the sky. It typically appears when sunlight passes through raindrops, causing the light to bend and separate into different colors. The seven main colors of a rainbow are red, orange, yellow, green, blue, indigo, and violet. These colors can be remembered using the acronym ROYGBIV, which stands for the first letter of each color. Each color blends into the next, creating a beautiful arc that can often be seen after a rain shower when the sun shines.