Indigo

This article is about the color. For the Indian airline, see IndiGo. For other uses, see Indigo (disambiguation).

Indigo
A piece of indigo plant dye from India, about 2.5 inches (6 cm) square
Wavelength	450–420(disputed) nm
Common connotations
loyalty, religion, spirituality, intuition, sorcery
Color coordinates
Hex triplet	#4B0082
sRGBB  (r, g, b)	(75, 0, 130)
CMYKH   (c, m, y, k)	(42, 100, 0, 49)
HSV       (h, s, v)	(275°, 100%, 51%)
Source	HTML/CSS
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

Indigo is a color that is traditionally regarded as a color on the visible spectrum, as well as one of the seven colors of the rainbow: the color between blue and violet. Although traditionally considered one of seven major spectral colors, sources differ as to its actual position in the electromagnetic spectrum. Indigo is a deep and bright color close to the color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine.

The color indigo was named after the indigo dye derived from the plant Indigofera tinctoria and related species.

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

History

Extract of natural indigo applied to paper

India is believed to be the oldest center of indigo dyeing in the Old World. It was a primary supplier of indigo dye, derived from the plant Indigofera tinctoria, to Europe as early as the Greco-Roman era. The association of India with indigo is reflected in the Greek word for the 'dye', which was indikon (ινδικόν). The Romans used the term indicum, which passed into Italian dialect and eventually into English as the word indigo. El Salvador has lately been the biggest producer of indigo.

The same indigo dye is contained in the woad plant, Isatis tinctoria, for a long time the main source of blue dye in Europe. Woad was replaced by true indigo as trade routes opened up, and both are now largely replaced by synthetic dyes.

Though the word indigo has existed in English since the 13th century, it may never have been a common part of the basic color-naming system.

Classification as a spectral color

Indigo is one of the colors on Newton's color wheel

Many modern books place indigo on the spectrum between 450 and 420 nanometers, which lies on the short-wave side of color wheel (RGB) blue, towards (spectral) violet. However, the correspondence of this definition with colors of actual indigo dyes is disputed. Optical scientists Hardy and Perrin list indigo as between 446 and 464 nm wavelength, which occupies a spectrum segment from roughly the color wheel (RGB) blue extending to the long-wave side, towards azure.

Isaac Newton introduced indigo as one of the seven colors in his spectrum. In the mid-1660s, when Newton bought a pair of prisms at a fair near Cambridge, the East India Company had begun importing indigo dye into England, supplanting the homegrown woad as the source of blue dye. In a pivotal experiment in the history 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 this optical spectrum, Newton acknowledged that the spectrum had a continuum of colors, but named seven colors: "The originall or primary colours are Red, yellow, Green, Blew, & a violet purple; together with Orang, Indico, & an indefinite varietie of intermediate gradations." He linked the seven prismatic colors to the seven notes of a western major scale, as shown in his color wheel, with orange and indigo as the semitones. 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 will show that "Indigo" corresponds to blue, while "Blue" corresponds to cyan.

"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."

Traditional 7 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 mnemonic Roy G. Biv. James Clerk Maxwell and Hermann von Helmholtz accepted indigo as an appropriate name for the color flanking violet in the spectrum.

Later scientists conclude that Newton named the colors differently from current usage. 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 name blue-green or cyan." If this is true, Newton's seven spectral colors would have been:

Red:     Orange:     Yellow:     Green:     Blue:     Indigo:     Violet:    

The human eye does not readily differentiate hues in the wavelengths between blue and violet. If this is where Newton meant indigo to lie, most individuals would have difficulty distinguishing indigo from its neighbors. According to Isaac 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."

Modern color scientists typically divide the spectrum between violet and blue at about 450 nm, with no indigo.

Distinction between the four major tones of indigo

Like many other colors (orange, rose, and violet are the best-known), indigo gets its name from an object in the natural world—the plant named indigo once used for dyeing cloth (see also Indigo dye).

The color 'electric indigo' is a bright and saturated color between the traditional indigo and violet. This is the brightest color indigo that can be approximated on a computer screen—it is a color located between the (primary) blue and the color violet on 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.

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 color midnight blue.

Below are displayed these four major tones of indigo. When specifying the color indigo, it is important to indicate which of these four major tones is desired.

Electric indigo

Electric Indigo
Color coordinates
Hex triplet	#6F00FF
sRGBB  (r, g, b)	(111, 0, 255)
CMYKH   (c, m, y, k)	(57, 100, 0, 0)
HSV       (h, s, v)	(266°, 100%, 100%)
Source	[1]
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

The color 'electric indigo' is much brighter than the pigment indigo reproduced below. When plotted on the CIE 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 the gamut of the sRGB color system.

Deep indigo (web color blue-violet)

Blue-Violet
Color coordinates
Hex triplet	#8A2BE2
sRGBB  (r, g, b)	(138, 43, 226)
CMYKH   (c, m, y, k)	(63, 81, 0, 0)
HSV       (h, s, v)	(271°, 81%, 89%)
Source	X11
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

At right is displayed the web color 'blue-violet', a color intermediate in brightness between electric indigo and pigment indigo. This color is also called 'deep indigo'.

Light indigo (web color indigo)

Indigo
Color coordinates
Hex triplet	#4B0082
sRGBB  (r, g, b)	(75, 0, 130)
CMYKH   (c, m, y, k)	(42, 100, 0, 49)
HSV       (h, s, v)	(275°, 100%, 50%)
Source	X11
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

The color box at right displays the web color indigo which is equivalent to 'light indigo', the color indigo as it would be reproduced by artists' paints as opposed to the brighter indigo above (electric indigo) that is possible to reproduce on a computer screen. Its hue is closer to violet than to indigo dye for which the color is named. Pigment indigo can be obtained by mixing 55% pigment cyan with about 45% pigment magenta.

Compare the subtractive colors to the additive colors in the two primary color charts in the article on primary colors to see the distinction between electric colors as reproducible from light on a computer screen (additive colors) and the pigment colors reproducible with pigments (subtractive colors); the additive colors are significantly brighter because they are produced from light instead of pigment.

Light indigo (web color indigo) represents the way the color indigo was always reproduced in pigments, paints, or colored pencils in the 1950s. By the 1970s, because of the advent of psychedelic art, artists became used to brighter pigments, and pigments called "bright indigo" or "bright blue-violet" that are the pigment equivalent of the electric indigo reproduced in the section above became available in artists' pigments and colored pencils.

Tropical indigo

Tropical Indigo
Color coordinates
Hex triplet	#9683EC
sRGBB  (r, g, b)	(150, 131, 236)
CMYKH   (c, m, y, k)	(48, 51, 0, 0)
HSV       (h, s, v)	(251°, 44%, 93%)
Source	Gallego and Sanz
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

'Tropical Indigo' is the color that is called añil (the Spanish word for "tropical indigo") in the Guía de coloraciones (Guide to colorations) by Rosa Gallego and Juan Carlos Sanz, a color dictionary published in 2005 that is widely popular in the Hispanophone realm.

Additional variations of indigo

Bright indigo

Indigo (Crayola)
Color coordinates
Hex triplet	#5D76CB
sRGBB  (r, g, b)	(93, 96, 189)
CMYKH   (c, m, y, k)	(54, 42, 0, 20)
HSV       (h, s, v)	(226°, 54%, 80%)
Source	Crayola
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

At right is displayed the 'bright indigo' color called 'indigo' in Crayola crayons. This color was added by Crayola in 1999.

Denim

Denim
Color coordinates
Hex triplet	#1560BD
sRGBB  (r, g, b)	(21, 96, 189)
CMYKH   (c, m, y, k)	(89, 49, 0, 26)
HSV       (h, s, v)	(213°, 89%, 74%)
Source	Crayola
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

'Denim' is a tone of indigo Crayola which resembles the shade of indigo used in denim. Crayola created this color in 1993 as one of the new 16 colors. Denim is the color of denim cloth, which after being dyed with indigo dye, is used to make jeans.

The Denim Revolution is a term used by the radical opposition in Belarus and their supporters in the West, who support a color revolution to implement the reintroduction of democracy, to describe their effort and aspirations.

In the 1960s, denim symbolized youth culture because so many young baby boomers wore denim jeans.

Violet-blue

Violet-Blue
Color coordinates
Hex triplet	#324AB2
sRGBB  (r, g, b)	(50, 74, 178)
CMYKH   (c, m, y, k)	(71, 58, 0, 30)
HSV       (h, s, v)	(229°, 72%, 70%)
Source	Crayola
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

The color 'violet-blue' is a bluish tone of blue-violet. The Crayola color called 'violet-blue' is displayed at right. The Crayola crayon color called "violet-blue" was formulated in 1958 and continued as a Crayola color until 1990.

Imperial blue

Imperial Standard of Napoleon I

See also Imperial red

Imperial Blue
Color coordinates
Hex triplet	#002395
sRGBB  (r, g, b)	(0, 35, 149)
CMYKH   (c, m, y, k)	(100, 77, 0, 42)
HSV       (h, s, v)	(226°, 100%, 58%)
Source	Vexillological
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

At right is displayed the color 'imperial blue'. Imperial blue is a representation of the blue color of the Imperial Standard of Napoleon I.

The first recorded use of 'imperial blue' as a color name in English was in the 1820s (exact year uncertain).

Persian indigo

Main article: Persian blue § Persian indigo

Persian Indigo
Color coordinates
Hex triplet	#32127A
sRGBB  (r, g, b)	(50, 18, 122)
CMYKH   (c, m, y, k)	(96, 100, 16, 11)
HSV       (h, s, v)	(258°, 85%, 48%)
Source	[2]/Maerz and Paul
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

The color 'Persian indigo' is displayed at right. Another name for this color (seldom used nowadays) is 'regimental'. The color was called regimental because in the 19th century it was commonly used by many nations for navy uniforms. 'Persian indigo' is named for an association with a product from Persia: Persian cloth dyed with indigo dye.

The first recorded use of 'regimental' (the original name for the color now called Persian indigo) as a color name in English was in 1912.

Midnight blue

Main article: Midnight blue

Midnight Blue
Color coordinates
Hex triplet	#191970
sRGBB  (r, g, b)	(25, 25, 112)
CMYKH   (c, m, y, k)	(97, 78, 39, 29)
HSV       (h, s, v)	(240°, 78%, 44%)
Source	X11
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

At right is displayed the web color 'midnight blue'.

Dark imperial blue

Imperial Blue (ISCC-NBS)
Color coordinates
Hex triplet	#00416A
sRGBB  (r, g, b)	(0, 65, 106)
HSV       (h, s, v)	(203°, 100%, 42%)
Source	ISCC-NBS
B: Normalized to [0–255] (byte)

The color 'dark imperial blue' is called 'imperial blue' on the ISCC-NBS color list.It also relates to a colour similar to itself its called indigo póo a colour name after a place in northern Spain in Austria

Japanese indigo

Indigo (JTC)
Color coordinates
Hex triplet	#264348
sRGBB  (r, g, b)	(38, 67, 72)
CMYKH   (c, m, y, k)	(47, 7, 0, 72)
HSV       (h, s, v)	(189°, 47%, 28%)
Source	JTC
B: Normalized to [0–255] (byte) H: Normalized to [0–100] (hundred)

The color 'Japanese indigo' is shown at right. This is the color that is called 'indigo' in the Japanese traditional colors, a group of colors in use beginning in 660 CE in the form of various dyes used in designing kimonos.

The name of this color in Japanese is ai-iro, which means indigo color.

In nature

Fungi

• Lactarius indigo is one of the very few species of mushrooms colored in tones of blue.

Birds

• Male indigobirds are a very dark, metallic blue.
• The indigo bunting, native to North America, is mostly bright cerulean blue with an indigo head. The related blue grosbeak is, ironically, more indigo than the indigo bunting.

Snakes

• The eastern indigo snake, Drymarchon couperi, of the southeastern United States, is a dark blue/black.

In culture

Business

• Indigo Books and Music uses an indigo logo and has sometimes referred to the color as "blue" in advertising.
• IndiGo Airlines is an Indian budget airlines that uses an indigo logo and it operates only Airbus A320s.

Computer graphics

• Electric indigo is sometimes used as a glow color for computer graphics lighting, possibly because it seems to change color from indigo to lavender when blended with white.

Food

• Scientists discovered in 2008 that when a banana becomes ripe and ready to eat, it glows bright indigo under a black light. Some insects, as well as birds and bats, may see into the ultraviolet because they are tetrachromats, and can use this information to tell when a banana is ripe and ready to eat. The glow is the result of a chemical created as the green chlorophyll in the peel breaks down.

Dyes

Indigo is created in potholes carved in pumice "tufgrond" in Karoland, Sumatra

• In Mexico, indigo is known as 'añil'. After silver and cochineal to produce red, añil was the most important product to be exported by historical Mexico.
• Guatemala, as of 1778, was considered one of the world's foremost provider of indigo.

Music

• "Mood Indigo" (1930) is a jazz composition and song, with music by Duke Ellington and Barney Bigard with lyrics by Irving Mills.
• The Indigo Girls are a folk duo.
• The Indigo Kings are a six-piece jazzy blues and vintage pop band from the UK.
• "Indigo" is a song by Peter Gabriel from the album Peter Gabriel (1978 album) (1978).
• "Indigo Eyes" is a song by Peter Murphy.
• "Indigo" is a song by the duo Moloko from their album Things to Make and Do (2000).
• "Indigo is Blue" is a tautological song by Catherine Wheel.
• "Indigo Children" is a song by Puscifer from the album "V" Is for Vagina (2007).
• "Indigoism" is an album by The Underachivers (2013).
• "Turbulent Indigo" is an album by Joni Mitchell (1994).
• "Wit a Indigo" is a song and music video by recording artist Willow Smith. (2015).

Spirituality

The tone of indigo used in the spiritualist applications is electric indigo because the color is represented as being the color of the spectrum between blue and violet.

• The color electric indigo is used in New Age philosophy to symbolically represent the sixth chakra (called Ajna), which is said to include the third eye. This chakra is believed to be related to intuition and gnosis (spiritual knowledge).
• Alice A. Bailey used indigo as the "second ray", representing "Love-Wisdom", in her Seven Rays system classifying people into seven metaphysical psychological types.
• Psychics often associate indigo paranormal auras with an interest in religion or with intense spirituality and intuition. Indigo children are said to have predominantly indigo auras. People with indigo auras are said to favor occupations such as computer analyst, animal caretaker, and counselor.

See also

• List of colors
• Rainbow – indigo is usually the sixth listed color of the rainbow
• Indiglo, a brand name for a method of electroluminescence technology
• Indigofera, a genus of flowering plants
• Baptisia (false indigo), a genus of flowering plants