Why are rainbows different colors?

Question

Why are rainbows different colors?

Answer 1

Geoff is right. Light is a spectra. As it passes through elements (every element casts a different light spectra), you see color. Rainbows are sun light that appear in the sky when the Sun shines onto droplets of moisture in the Earth's atmosphere.

The sky appears blue because as the suns light reaches our atmosphere, all the colors scatter except the blue, so blue is all we see.

Answer 2

The light is separated into it's constituent colours by refraction.  The index of refraction of a substance is a function of frequency (dispersion) and so different colours are bent at different angles.  This results in the light being separated into the different colours of the rainbow.