Indigo is a term used for a number ofhues in the region ofblue. The word comes from theancient 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 sevencolors of the rainbow as described by Newton, or a region on thecolor 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" inHTML web page specifications.
The word "indigo" comes from the Latin wordindicum, meaning "Indian", as the naturally based dye was originally exported to Europe fromIndia.
The first known recorded use of indigo as a color name inEnglish was in 1289.[4]
Isaac Newton regarded indigo as a color in thevisible spectrum, as well as one of the seven colors of therainbow: the color betweenblue andviolet; however, sources differ as to its actual position in theelectromagnetic spectrum. Later scientists have concluded that what Newton called "blue" was what is now calledcyan 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 theAbney effect, pinpointing indigo to a specific hue value in theHSV color wheel is elusive, as a higher HSV saturation value shifts the hue towards blue. However, on the newCIECAM16 standard, the hues values around 290° may be thought of as indigo, depending on the observer.
Indigofera tinctoria and related species were cultivated inEast Asia,Egypt,India,Bangladesh andPeru in antiquity. The earliest direct evidence for the use of indigo dates to around 4000 BC and comes fromHuaca Prieta, in contemporary Peru.[5]Pliny the Elder mentions India as the source of the dye after which it was named.[6] It was imported from there in small quantities via theSilk Road.[7]
TheAncient Greek term for the dye wasἸνδικὸν φάρμακον (indikon pharmakon, "Indiandye"), which, adopted toLatin asindicum (asecond declension noun) orindico (oblique case) and viaPortuguese, gave rise to the modern wordindigo.[8]
Indigo extracted from woad
In early Europe, the main source was from the woad plantIsatis tinctoria, also known as pastel.[9] For a long time, woad was the main source of blue dye in Europe. Woad was replaced by "true indigo", as trade routes opened up. Plant sources have now been largely replaced bysynthetic dyes.
Spanish explorers discovered an American species of indigo and began to cultivate the product inGuatemala. The English and French subsequently began to encourage indigo cultivation in their colonies in theWest Indies.[10]
In North America, indigo was introduced byEliza Lucas into colonial South Carolina, where it became the colony's second-most importantcash crop (after rice).[11] Before theRevolutionary War, indigo accounted for more than one-third of the value of exports from the American colonies.[12]
Isaac Newton's classification of indigo as a spectral color
Indigo is one of the colors on Newton'scolor wheel.
Isaac Newton introduced indigo as one of the seven base colors of his work. In the mid-1660s, when Newton bought a pair ofprisms at a fair nearCambridge, theEast India Company had begun importing indigo dye into England,[13] supplanting the homegrownwoad as source of blue dye. In a pivotal experiment in thehistory of optics,the young Newton shone a narrow beam of sunlight through a prism to produce a rainbow-like band of colors on the wall. In describing thisoptical spectrum, Newton acknowledged that the spectrum had a continuum of colors, but named seven: "The originall or primary colours are Red, yellow, Green, Blew, & a violet purple; together with Orang, Indico, & an indefinite varietie of intermediate gradations."[14] He linked the seven prismatic colors to the seven notes of a westernmajor scale,[15] as shown in his color wheel, with orange and indigo as thesemitones. Having decided upon seven colors, he asked a friend to repeatedly divide up the spectrum that was projected from the prism onto the wall:
Newton's observation of prismatic colors: Comparing this to a color image of the visible light spectrum shows that "blue" corresponds tocyan, while "indigo" corresponds toblue.
I desired a friend to draw with a pencil lines cross the image, or pillar of colours, where every one of the seven aforenamed colours was most full and brisk, and also where he judged the truest confines of them to be, whilst I held the paper so, that the said image might fall within a certain compass marked on it. And this I did, partly because my own eyes are not very critical in distinguishing colours, partly because another, to whom I had not communicated my thoughts about this matter, could have nothing but his eyes to determine his fancy in making those marks.[16]
The traditional seven colors of the rainbow
Indigo is therefore counted as one of the traditional colors of the rainbow, the order of which is given by the mnemonics "Richard of York gave battle in vain" andRoy G. Biv.James Clerk Maxwell andHermann von Helmholtz accepted indigo as an appropriate name for the color flanking violet in the spectrum.[17]
Later scientists concluded that Newton named the colors differently from current usage.[18][19]According to Gary Waldman, "A careful reading of Newton's work indicates that the color he called indigo, we would normally call blue; his blue is then what we would nameblue-green orcyan."[20] If this is true, Newton's seven spectral colors would have been:
The human eye does not readily differentiate hues in the wavelengths between what are now called blue and violet.[citation needed] If this is where Newton meant indigo to lie, most individuals would have difficulty distinguishing indigo from its neighbors. According toIsaac Asimov, "It is customary to list indigo as a color lying between blue and violet, but it has never seemed to me that indigo is worth the dignity of being considered a separate color. To my eyes, it seems merely deep blue."[21]
In 1821,Abraham Werner publishedWerner's Nomenclature of Colours, where indigo, calledindigo blue, is classified as a blue hue, and not listed among the violet hues. He writes that the color is composed of "Berlin blue, a little black, and a small portion of apple green," and indicating it is the color of bluecopper ore, with Berlin blue being described as the color of ablue jay's wing, ahepatica flower, or a bluesapphire.[22]
According to an article,Definition of the Color Indigo published inNature magazine in the late 1800s, Newton's use of the term "indigo" referred to a spectral color between blue and violet. However, the article states that Wilhelm von Bezold, in his treatise on color, disagreed with Newton's use of the term, on the basis that the pigment indigo was a darker hue than the spectral color; and furthermore, ProfessorOgden Rood points out that indigo pigment corresponds to the cyan-blue region of the spectrum, lying between blue and green, although darker in hue. Rood considers that artificialultramarine pigment is closer to the point of the spectrum described as "indigo", and proposed renaming that spectral point as "ultramarine". The article goes on to state that comparison of the pigments, both dry and wet, with Maxwell's discs and with the spectrum, that indigo is almost identical toPrussian blue, stating that it "certainly does not lie on the violet side of 'blue.'" When scraped, a lump of indigo pigment appears more violet, and if powdered or dissolved, becomes greenish.[23]
The correspondence of this definition with colors of actual indigo dyes, though, is disputed. Optical scientists Hardy and Perrin list indigo as between 445[26] and 464 nm wavelength,[27] which occupies a spectrum segment from roughly the color wheel (RGB) blue extending to the long-wave side, towardsazure.
Other moderncolor scientists, such as Bohren and Clothiaux (2006), and J.W.G. Hunt (1980), divide the spectrum between violet and blue at about 450 nm, with no hue specifically named indigo.[28][29]
Towards the end of the 20th century, purple colors also became referred to as "indigo". In the 1980s, computer programmersJim Gettys, Paul Ravelling, John C. Thomas and Jim Fulton produced a list of colors for theX Window Operating System. The color identified as "indigo" was not the color indigo (as generally understood at the time), but was actually a dark purple hue; the programmers assigned it thehex code #4B0082. This collection of color names was somewhat arbitrary: Thomas used a box of 72Crayola crayons as a standard, whereas Ravelling used color swabs from the now-defunct Sinclair Paints company, resulting in the color list for versionX11 of the operating system containing fanciful color names such as "papaya whip", "blanched almond" and "peach puff". The database was also criticised for its many inconsistencies, such as "dark gray" being lighter than "gray", and for the color distribution being uneven, tending towards reds and greens at the expense of blues.[30]
In the 1990s, this list which came with version X11 became the basis of theHTML andCSS color rendition used in websites and web design. This resulted in the name "Indigo" being associated with purple and violet hues in web page design and graphic design. Physics author John Spacey writes on the websiteSimplicable that the X11 programmers did not have any background in color theory, and that as these names are used by web designers and graphic designers, the nameindigo has since that time been strongly associated with purple or violet. Spacey writes, "As such, a few programmers accidentally repurposed a color name that was known to civilisations for thousands of years."[31]
The Crayola company released anindigo crayon in 1999, with the Crayola website using thehex code #4F49C6 toapproximate the crayon color. The 2001 iron indigo crayon is portrayed using hex code #184FA1. The 2004 indigo crayon color is depicted by #5D76CB, and the 2019 iridescent indigo is portrayed by #3C32CD.
Like many other colors (orange,rose, andviolet are the best-known), indigo gets its name from an object in the natural world—the plant namedindigo once used for dyeing cloth (see alsoIndigo dye).
The color pigment indigo is equivalent to the web color indigo and approximates the color indigo that is usually reproduced in pigments and colored pencils.
The color of indigo dye is a different color from either spectrum indigo or pigment indigo. This is the actual color of the dye. A vat full of this dye is a darker color, approximating the web colormidnight blue.
The color "electric indigo" is a bright andsaturated color between the traditional indigo and violet. This is thebrightest color indigo that can be approximated on a computer screen; it is a color located between the (primary) blue and the colorviolet of the RGB color wheel.
The web color blue violet or deep indigo is a tone of indigo brighter than pigment indigo, but not as bright as electric indigo.
Listed below are several indigo hues, some of which have included the word "indigo", with the adoption ofHTML color names in theWorld Wide Web era.
Indigo dye is a greenish dark blue color, obtained from either the leaves of the tropical Indigo plant (Indigofera), or from woad (Isatis tinctoria), or the Chinese indigo (Persicaria tinctoria). Many societies make use of theIndigofera plant for producing different shades of blue. Cloth that is repeatedly boiled in an indigo dye bath-solution (boiled and left to dry, boiled and left to dry, etc.), the blue pigment becomes darker on the cloth. After dyeing, the cloth is hung in the open air to dry.
A Native American woman described the process used by theCherokee Indians when extracting the dye:
We raised our indigo which we cut in the morning while the dew was still on it; then we put it in a tub and soaked it overnight, and the next day we foamed it up by beating it with a gourd. We let it stand overnight again, and the next day rubbedtallow on our hands to kill the foam. Afterwards, we poured the water off, and the sediment left in the bottom we would pour into a pitcher or crock to let it get dry, and then we would put it into a poke made of cloth (i.e. sack made of coarse cloth) and then when we wanted any of it to dye [there]with, we would take the dry indigo.[33][34]
InSa Pa, Vietnam, the tropical Indigo (Indigo tinctoria) leaves are harvested and, while still fresh, placed inside a tub of room-temperature to lukewarm water where they are left to sit for 3 to 4 days and allowed to ferment, until the water turns green. Afterwards, crushed limestone (pickling lime) is added to the water, at which time the water with the leaves are vigorously agitated for 15 to 20 minutes, until the water turns blue. The blue pigment settles as sediment at the bottom of the tub. The sediment is scooped out and stored. When dyeing cloth, the pigment is then boiled in a vat of water; the cloth (usually made from yarns ofhemp) is inserted into the vat for absorbing the dye. After hanging out to dry, the boiling process is repeated as often as needed to produce a darker color.
In aRGB color space, "Indigo(color wheel)" is composed of 25.1%red, 0%green and 100%blue. Whereas in a CMYK color space, it is composed of 74.9%cyan, 100%magenta, 0%yellow and 0%black. It has a hue angle of 255.1 degrees, a saturation of 100% and a lightness of 50%. Indigo(color wheel) could be obtained by blendingviolet withblue.
"Electric indigo" is brighter than the pigment indigo reproduced above. When plotted on theCIE chromaticity diagram, this color is at 435 nanometers, in the middle of the portion of the spectrum traditionally considered indigo, i.e., between 450 and 420 nanometers. This color is only an approximation of spectral indigo, since actual spectral colors are outside thegamut of thesRGB color system.
At right is displayed the web color "blue-violet", a color intermediate in brightness between electric indigo and pigment indigo. It is also known as "deep indigo".
'Tropical Indigo' is the color that is calledañil in theGuía de coloraciones (Guide to colorations) by Rosa Gallego andJuan Carlos Sanz, a color dictionary published in 2005 that is widely popular[according to whom?] in theHispanophone realm.
Electric indigo is sometimes used as a glow color forcomputer graphics lighting, possibly because it seems to change color from indigo tolavender when blended with white.
Indigo is created in potholes carved in pumice "tufgrond" inKaroland,Sumatra.
Indigo dye was used to dye denim, giving the original 'blue jeans' their distinctive colour.
The original Postal Worker uniform contained indigo dye, partly due to the dye not running when wet.[40]
Guatemala, as of 1778, was considered one of the world's foremost providers of indigo.[41]
In Mexico, indigo is known asañil.[42] After silver, andcochineal to produce red,añil was the most important product exported by historical Mexico.[43]
The use ofañil is survived in the Philippines, particularly in the Visayas and Mindanao. The powder dye is mixed with vinegar to be applied to the cheek of a person suffering from mumps.[citation needed]
Scientists discovered in 2008 that when abanana becomes ripe, it glows bright indigo under ablack light. Some insects, as well as birds, see into theultraviolet, because they aretetrachromats and can use this information to tell when a banana is ready to eat. The glow is the result of a chemical created as the greenchlorophyll in the peel breaks down.[44]
TheFrench Army adopted dark blue indigo at the time of theFrench Revolution, as a replacement for the white uniforms previously worn by the Royal infantry regiments. In 1806,Napoleon decided to restore the white coats because of shortages ofindigo dye imposed by the British continental blockade. However, the greater practicability of the blue color led to its retention, and indigo remained the dominant color of French military coats until 1914.[citation needed]
In theBetter Call Saul episode "Hero", Howard Hamlin mentions that his law firm Hamlin Hamlin & McGill trademarked a colour called "Hamlindigo" whilst confronting Jimmy McGill over trademark infringement in a billboard advertisement he produced for his own legal services.
The color electric indigo is used inNew Age philosophy to symbolically represent the sixthchakra (calledAjna), which is said to include thethird eye. Thischakra is believed to be related tointuition andgnosis (spiritual knowledge).[46][47]
^Ottenheimer, Harriet Joseph (2009).The anthropology of language: an introduction to linguistic anthropology (2nd ed.). Belmont, CA: Wadsworth. p. 29.ISBN978-0-495-50884-7.
^Maerz and PaulA Dictionary of Color New York:1930 McGraw-Hill Page 197; Color Sample of Indigo: Page 117 Plate 47 Color Sample E10
^Clark, Robin J. H.; Cooksey, Christopher J.; Daniels, Marcus A. M.; Withnall, Robert (1993). "Indigo, woad, and Tyrian Purple: important vat dyes from antiquity to the present".Endeavour.17 (4):191–199.doi:10.1016/0160-9327(93)90062-8.
^ἸνδικόςArchived 29 January 2021 at theWayback Machine in Henry George Liddell. Robert Scott. A Greek-English Lexicon. revised and augmented throughout by. Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie. Oxford. Clarendon Press. 1940; Englishindigo since the 17th century, changed from 16th-centuryindico.
^Allen, O.N. Allen & Ethel K. (1981).The Leguminosae: a source book of characteristics, uses, and nodulation (null ed.). Madison, Wisc.: University of Wisconsin Press. p. 343.ISBN978-0-299-08400-4.
^"Definition of the Color Indigo".Littel's Living Age.145 (1869). 1880.Archived from the original on 30 October 2023. Retrieved30 October 2023.Newton denoted by the name of "indigo" the tint of the spectrum lying between "blue" and "violet." Von Bezold, in his work on color, rejects the term, justifying his objection by observing that the pigment indigo is a much darker hue than the spectrum tint. Prof. O. N. Rood, who follows Von Bezold in rejecting the term, brings forward the further objection that the tint of the pigment indigo more nearly corresponds in hue (though it is darker) with the cyan-blue region lying between green and blue. By comparing the tints of indigo pigment, both dry and wet, with the spectrum, and by means of Maxwell's disks, it appears that the hue of indigo is almost identical with that of Prussian blue, and certainly does not lie on the violet side of "blue." Indigo in the dry lump, if scraped, has, however, a more violet tint; but if fractured or powdered, or dissolved, its tint is distinctly greenish. Prof. Rood considers that artificial ultramarine corresponds much more nearly to the true tint of the spectrum at the point usually termed "indigo," and he therefore proposes to substitute the term "ultramarine" in its place, the color of the artificial pigment being thereby intended.
^Spacey, John (19 June 2020)."19 Types of Indigo".Simplicable.Archived from the original on 5 June 2023. Retrieved30 October 2023.In 1986 some programmers created a list of color names for a unix system known as X11. Having no background in color theory, they placed indigo as a dark purple. This list was later used by HTML and CSS standards that remain in place to this day. These standards are used by millions of designers and digital artists such that the color name indigo is now strongly associated with dark purple or violet. As such, a few programmers accidentally repurposed a color name that was known to civilizations for thousands of years. ...Note the difference between Web Indigo and Indigo. This standard color name is completely detached from the traditional color. This misrepresentation resulted from the random selection by a programmer working on an operating system in 1986.
^Knight, Oliver (1956–57), "History of the Cherokees, 1830–1846",Chronicles of Oklahoma, Oklahoma City: Oklahoma Historical Society, p. 164,OCLC647927893
^Gallego, Rosa; Sanz, Juan Carlos (2005).Guía de coloraciones (Gallego, Rosa; Sanz, Juan Carlos (2005).Guide to Colorations) Madrid: H. Blume.ISBN84-89840-31-8
^"It's New and It's Blue" (Indigo advertisement),The Globe and Mail, Toronto, 1 October 1999, p. A3
^Tansley, David W.Subtle Body: Essence and Shadow 1984 (Art and Cosmos Series--Jill Purce, editor)
^Stevens, Samantha. The Seven Rays: a Universal Guide to the Archangels. City: Insomniac Press, 2004.ISBN1-894663-49-7 pg. 24
^Graham, Lanier F. (editor)The Rainbow Book Berkeley, California:1976 Shambala Publishing and The Fine Arts Museums of San Francisco (Handbook for the Summer 1976 exhibitionThe Rainbow Art Show which took place primarily at theDe Young Museum, but also at other museums)Indigo Pages 152–153 The color indigo is stated to represent intuition.
