Indigo is made of purple and blue and is named from the indigo plant, which is used to make indigo dye. Sir Isaac Newton included indigo in the rainbow color scheme, and it is the only tertiary color in his color wheel.
Sir Isaac Newton incorporated indigo into his rainbow color wheel, which included six other colors: red, orange, yellow, green, blue and violet.
Indigo refers both to the blue pigment used as a dye and to indigo plants. Indigo dye has been used for thousands of years by civilizations all over the world to dye fabric blue. It is the most widely used natural dye in history.