Indigo dye is an organic compound with a distinctive blue color. Indigo is a natural dye extracted from the leaves of some plants of the Indigofera genus, in particular Indigofera tinctoria. Dye-bearing Indigofera plants were commonly grown and used throughout the world, particularly in Asia, with the production of indigo dyestuff economically important due to the historical rarity of other blue dyestuffs.
Indigo dye
Indigo, historical dye collection of the Technical University of Dresden, Germany
Cake of indigo, about 2 cm
Indigo factory at Allahabad, India, drawn by Émile Thérond [fr], 19th century
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 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.
A piece of indigo plant dye from India, about 6 cm (2.5 in) square
Indigo extracted from woad
Newton's observation of prismatic colors: Comparing this to a color image of the visible light spectrum shows that "blue" corresponds to cyan, while "indigo" corresponds to blue.
Indigo bunting