This article is about the color. For other meanings, see Indigo (disambiguation).

Indigo is the color of blue between 440 to 420 nanometres in wavelength, placing it between blue and violet. Light that contains both violet and blue frequencies is also indigo, but this is not how indigo is defined. Like many other colors (orange and violet are the most well-known), it gets its name from an object in the natural world - the plant named indigo once used for dyeing cloth (see also Indigo dye).

Indigo is neither an additive primary color nor a subtractive primary color. It was named and defined by Isaac Newton when he divided up the optical spectrum (which is a continuum of frequencies). He specifically named seven colors primarily to match the seven notes of a western musical scale, because he believed sound and light were physically similar, but also to link colours with the (known) planets, days of the week, and other lists that had seven items.

The human eye is relatively insensitive to indigo's frequencies, and some otherwise well-sighted people cannot distinguish indigo from blue and violet. For this reason some commentators including Isaac Asimov have suggested that indigo should not be regarded as a color in its own right but merely as a shade of blue or violet.

In ancient Mayan cultures indigo was the one color that was recognized for its soothing effect on pregnant women and their unborn children. Pregnant women often wore this color in order to protect themselves and their child from danger and to ensure a safe a successful delivery.

Web colors

See also

• List of colors
• Indigo dye

Optical spectrum

Indigo | Indigo (Farbton) | Añil | Indigo | Indigo | אינדיגו | Indigo (kleur) | インディゴ | Indigo | Indigo | Indigo | Chàm