Where is indigo on a color chart?

Indigo is located between blue and violet on the color chart. It occupies a wavelength along the visible spectrum between 440 and 450 nanometers and ranges in color from a deep dark blue to a rosy blue-violet.

Isaac Newton suggested adding indigo to the color spectrum, claiming he was able to observe it through experiments with his prism. Skeptics believe that Newton added the color to correlate with the seven audible musical notes. Color theorists who oppose including indigo on the color chart claim that it is not a

distinguishable color, and that it does not conform to accepted rules that govern the formation of secondary colors.