Indigo

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Indigo is a term used for a number of hues in the region of blue. The word comes from the ancient dye of the same name. The term "indigo" can refer to the color of the dye, various colors of fabric dyed with indigo dye, a spectral color, one of the seven colors of the rainbow as described by Isaac Newton, or a region on the color wheel, and can include various shades of blue, ultramarine, and green-blue. Since the web era, the term has also been used for various purple and violet hues identified as "indigo", based on use of the term "indigo" in HTML web page specifications.

The word "indigo" comes from the Latin word , meaning "Indian", as the naturally based dye was originally exported to Europe from India.

The Early Modern English word indigo referred to the dye, not to the color (hue) itself, and indigo is not traditionally part of the basic color-naming system.

The first known recorded use of indigo as a color name in English was in 1289.

Newton regarded indigo as a color in the visible spectrum, as well as one of the seven colors of the rainbow: the color between blue and violet; however, sources differ as to its actual position in the electromagnetic spectrum. Later scientists have concluded that what Newton called "blue" was what is now called cyan or blue-green; and what Newton called "indigo" was what is now called blue.

In the 1980s, programmers produced a somewhat arbitrary list of color names for the X Window computer operating system, resulting in the HTML and CSS specifications issued in the 1990s using the term "indigo" for a dark purple hue. This has resulted in violet and purple hues also being associated with the term "indigo" since that time.

Because of the Abney effect, pinpointing indigo to a specific hue value in the HSV color wheel is elusive, as a higher HSV saturation value shifts the hue towards blue. However, on the new CIECAM16 standard, the hues values around 290° may be thought of as indigo, depending on the observer. Provided by Wikipedia