Indigo

Indigo (pronounced in-di-goh)

(1) A blue dye obtained from various plants, especially of the genus Indigofera, or manufactured synthetically.

(2) A descriptor of color indigo, widely defined commercially and ranging from a deep violet blue to a dark, greyish blue (sometimes as "indigo blue").

(3) In technical use, as indigo blue (also casually referred to as indigotin or indigo), a dark-blue, water-insoluble, crystalline powder (C₁₆H₁₀N₂O₂), having a bronze-like luster, the essential coloring principle of which is contained along with other substances in the dye indigo and which can be produced synthetically.

(4) Any of numerous hairy plants belonging to the genus Indigofera, of the legume family, having pinnate leaves and clusters of usually red or purple flowers (the best-known of the plants including Amorpha (false indigo), Baptisia (wild indigo), and Psorothamnus and Dalea (indigo bush)).

(5) In zoology, as the Eastern indigo snake, the common name for the Drymarchon couperi.

(6) In zoology, as the indigobird (or indigo bird), any of various African passerine birds of the family Viduidae.

(7) A (rarely used) female given name.

1550s: The spelling change from indico to indigo happened in the 1550s, used originally in the sense of the “blue powder obtained from certain plants and used as a dye”.  Indigo was from the Spanish indico and the Portuguese endego (the Dutch indigo exclusively was from Portuguese), all from the Latin indicum (indigo), from the Ancient Greek ἰνδικόν (indikón) (Indian blue dye (literally “Indian substance”)), a neuter of indikos (Indian), from the Indic Ἰνδία (Indía).  Indic is a subgroup of the Indo-Iranian branch of Indo-European languages that includes Sanskrit, Hindi, Urdu, Bengali, and many other languages of India, Pakistan, and Sri Lanka; Indo-Aryan.  It replaced the late thirteenth century Middle English ynde, from the thirteenth century Old French inde (indigo; blue, violet), again from the Latin indicum; the earlier name in Mediterranean languages was annil or anil.  In the magical-realist novel Sassafrass, Cypress & Indigo (1982) by African American feminist Ntozake Shange (1948–2018), the name of one protagonist is Indigo and it continues to be used as a given name for females.  Indigo is a noun & adjective and indigotic is an adjective; the noun plural is indigos or indigoes.

Sir Issac Newton, light and the "two prism experiment" 

As used to refer to “the color of indigo”, use dates from the 1620s and in 1704 Sir Isaac Newton (1642–1727) adopted indigo as the name for the darkest of the two blues on his spectrum of the visible colors of light.  Newton identified seven colors in the spectrum of light (red, orange, yellow, green, blue, indigo and violet) and although he was a great figure of science and the Enlightenment, he was also an alchemist and theologian who published notable works of Biblical scholarship, something which may account for the choice of seven, that number being of some significance in scripture.  By objective analysis, there are probably six colors in the spectrum, but Newton’s world view which attributed something mystical to the number demanded there be seven.  He decided in advance light was made of seven colors but his experimental method to vindicate this theory of differential refraction was sound.  The orthodox view of the time suggested a prism acted on any incident light to add colour; Newton wished to prove what was really happening was a process of separation refraction.  For this, he used two prisms.  The first produced the full spectrum of colors and from this Newton isolated narrow beams of light of a single colour, directing them at the second prism, finding that for all colors, there was no further change as the beam passed through the second prism: “When any one sort of Rays hath been well parted from those of other kinds, it hath afterwards obstinately retained its colour, not with standing my utmost endeavours to change it.”

Lindsay Lohan shopping at Indigo Seas, North Robertson Boulevard, Los Angeles, February 2009.  Most fashion houses would regard her dress’s blue as “too blue” to be within the indigo range but to illustrate how far (in commercial use) indigo can travel from blue, some would call this "Spanish indigo" (Hex: #003C92; RGB: 0, 60, 148).

Although some use extends even to grey, generally, indigo is a range of bluish-purples between blue and violet in the color wheel and such is the reverence for Newton it’s considered still one of the seven spectral colors (indigo’s hex code is #4B0082),  In this, although it may visually be dubious, indigo has fared better than the unfortunate Pluto, the International Astronomical Union (IAU) voting in 2006 to re-classify Pluto as a dwarf planet on the basis the icy orb failed to meet a set of criteria which the IAU claimed had been accepted for decades.  The IAU are a bunch of humorless cosmic clerks, something like the Vogons ("...not actually evil, but bad-tempered, bureaucratic, officious and callous.") in Douglas Adams' (1952–2001) Hitchhiker's Guide to the Galaxy (1979-1992) and, not affected by romantic tales, have refused to restore Pluto to planethood, leaving it desolate, lonely and cold; it's the solar system’s emo.  Indigo place on the spectrum seems however secure and according to Canva (the internet’s authority on colors), it’s the color of devotion, wisdom, justice, and higher knowledge; tied to intuition and what is not seen; it is also considered spiritual.  More prosaically, Canva list indigo as hexadecimal #4b0082, with RGB values of Red: 29.4, Green: 0, Blue: 51 and CMYK values of Cyan: 0.42, Magenta: 1, Yellow: 0, Black (K):0.49.  The decimal value is 4915330.  It has a hue angle of 274.6 degrees, a saturation of 100% and a lightness of 25.5%. #4b0082 color hex could be obtained by blending #9600ff with #000005. Closest websafe color is: #330099.

Darker then violet: Canva's example of a classic indigo.