How many colors are in a rainbow?

There are seven traditional colors in a rainbow: red, orange, yellow, green, blue, indigo, and violet.

This familiar list is associated with Isaac Newton, who studied sunlight passing through glass prisms in the 17th century. Newton divided the visible spectrum into seven named color bands, partly influenced by the idea that nature should correspond to musical harmony. A rainbow itself forms when sunlight enters water droplets, bends, reflects inside them, and separates into different wavelengths as it leaves.

The colors do not actually appear as seven sharply separated stripes. They blend continuously across the visible spectrum, so scientists can describe many more shades between the traditional names. Indigo is also difficult to distinguish as a separate band for many viewers, but it remains part of the standard seven-color list taught in elementary science. Red has the longest visible wavelengths, while violet has the shortest.