Blue has been an important colour in art and decoration since ancient times. The semi-precious stonelapis lazuli was used in ancient Egypt for jewellery and ornament and later, in theRenaissance, to make the pigmentultramarine, the most expensive of all pigments.[3] In the eighth century Chinese artists usedcobalt blue to colour fineblue and white porcelain. In theMiddle Ages, European artists used it in the windows ofcathedrals. Europeans wore clothing coloured with the vegetable dyewoad until it was replaced by the finerindigo from America. In the 19th century, synthetic blue dyes and pigments gradually replaced organic dyes and mineral pigments. Dark blue became a common colour for military uniforms and later, in the late 20th century, for business suits. Because blue has commonly been associated with harmony, it was chosen as the colour of the flags of theUnited Nations and theEuropean Union.[4]
In the United States and Europe, blue is the colour that both men and women are most likely to choose as their favourite, with at least one recent survey showing the same across several other countries, including China, Malaysia, and Indonesia.[5][6] Past surveys in the US and Europe have found that blue is the colour most commonly associated withharmony,confidence,masculinity,knowledge,intelligence,calmness,distance,infinity, theimagination,cold, andsadness.[7]
InRussian,Mongolian,Irish, and some other languages, there is no single word for blue, but rather different words for light blue (Russian:голубой,goluboj) and dark blue (Russian:синий,sinij) (seeColour term).
Several languages, includingJapanese andLakota Sioux, use the same word to describe blue and green. For example, inVietnamese, the colour of both tree leaves and the sky isxanh. In Japanese, the word for blue (青,ao) is often used for colours that English speakers would refer to as green, such as the colour of atraffic signal meaning "go". In Lakota, the wordtȟó is used for both blue and green, the two colours not being distinguished in older Lakota (for more on this subject, seeBlue–green distinction in language).
Linguistic research indicates that languages do not begin by having a word for the colour blue.[10] Colour names often developed individually in natural languages, typically beginning withblack andwhite (or dark and light), and then addingred, and only much later – usually as the last main category of colour accepted in a language – adding the colour blue, probably when blue pigments could be manufactured reliably in the culture using that language.[10]
Optics and colour theory
The termblue generally describes colours perceived by humans observing light with adominant wavelength between approximately 450 and 495 nanometres.[11] Blues with a higher frequency and thus a shorter wavelength gradually look more violet, while those with a lower frequency and a longer wavelength gradually appear more green. Purer blues are in the middle of this range, e.g., around 470 nanometres.
Isaac Newton included blue as one of the seven colours in his first description of thevisible spectrum.[12] He chose seven colours because that was the number of notes in the musical scale, which he believed was related to the optical spectrum. He includedindigo, the hue between blue and violet, as one of the separate colours, though today it is usually considered a hue of blue.[13]
In painting and traditionalcolour theory, blue is one of the threeprimary colours of pigments (red, yellow, blue), which can be mixed to form a widegamut of colours. Red and blue mixed together form violet, blue and yellow together form green. Mixing all three primary colours together produces a dark brown. From the Renaissance onward, painters used this system to create their colours (seeRYB colour model).
The RYB model was used forcolour printing byJacob Christoph Le Blon as early as 1725. Later, printers discovered that more accurate colours could be created by using combinations of cyan, magenta, yellow, and black ink, put onto separate inked plates and then overlaid one at a time onto paper. This method could produce almost all the colours in thespectrum with reasonable accuracy.
Additive colour mixing. The combination ofprimary colours produces secondary colours where two overlap; the combination red, green, and blue each in full intensity makes white.
On theHSV colour wheel, thecomplement of blue isyellow; that is, a colour corresponding to an equal mixture ofred andgreen light. On a colour wheel based on traditional colour theory (RYB) where blue was considered a primary colour, its complementary colour is considered to beorange (based on theMunsell colour wheel).[14]
Lasers emitting in the blue region of the spectrum became widely available to the public in 2010 with the release of inexpensive high-powered 445–447 nmlaser diode technology.[22] Previously the blue wavelengths were accessible only throughDPSS which are comparatively expensive and inefficient, but still widely used by scientists for applications includingoptogenetics,Raman spectroscopy, andparticle image velocimetry, due to their superior beam quality.[23] Bluegas lasers are also still commonly used forholography,DNA sequencing,optical pumping, among other scientific and medical applications.
Blue is the colour of light betweenviolet andcyan on thevisible spectrum. Hues of blue include indigo andultramarine, closer to violet; pure blue, without any mixture of other colours; Azure, which is a lighter shade of blue, similar to the colour of the sky; Cyan, which is midway in the spectrum between blue andgreen, and the other blue-greens such asturquoise,teal, andaquamarine.
Blue also varies in shade or tint; darker shades of blue contain black or grey, while lighter tints contain white. Darker shades of blue include ultramarine,cobalt blue,navy blue, andPrussian blue; while lighter tints includesky blue,azure, andEgyptian blue (for a more complete list see theList of colours).
In nature, many blue phenomena arise fromstructural colouration, the result of interference between reflections from two or more surfaces ofthin films, combined with refraction as light enters and exits such films. The geometry then determines that at certain angles, the light reflected from both surfaces interferes constructively, while at other angles, the light interferes destructively. Diverse colours therefore appear despite the absence of colourants.[24]
Egyptian blue, the first artificial pigment, was produced in the third millennium BC in Ancient Egypt. It is produced by heating pulverized sand, copper, andnatron. It was used in tomb paintings and funereal objects to protect the dead in their afterlife. Prior to the 1700s, blue colourants for artwork were mainly based on lapis lazuli and the related mineral ultramarine. A breakthrough occurred in 1709 when German druggist and pigment makerJohann Jacob Diesbach discoveredPrussian blue. The new blue arose from experiments involving heating dried blood with iron sulphides and was initially called Berliner Blau. By 1710 it was being used by the French painterAntoine Watteau, and later his successorNicolas Lancret. It became immensely popular for the manufacture of wallpaper, and in the 19th century was widely used by French impressionist painters.[25] Beginning in the 1820s, Prussian blue was imported into Japan through the port ofNagasaki. It was calledbero-ai, or Berlin blue, and it became popular because it did not fade like traditional Japanese blue pigment,ai-gami, made from thedayflower. Prussian blue was used by bothHokusai, in his wave paintings, andHiroshige.[26]
In 1799 a French chemist,Louis Jacques Thénard, made a synthetic cobalt blue pigment which became immensely popular with painters.
In 1824 theSocieté pour l'Encouragement d'Industrie in France offered a prize for the invention of an artificialultramarine which could rival the natural colour made from lapis lazuli. The prize was won in 1826 by a chemist named Jean Baptiste Guimet, but he refused to reveal the formula of his colour. In 1828, another scientist,Christian Gmelin then a professor of chemistry in Tübingen, found the process and published his formula. This was the beginning of new industry to manufacture artificial ultramarine, which eventually almost completely replaced the natural product.[27]
In 1878 German chemists synthesizedindigo. This product rapidly replaced natural indigo, wiping out vast farms growing indigo. It is now the blue of blue jeans. As the pace oforganic chemistry accelerated, a succession of synthetic blue dyes were discovered includingIndanthrone blue, which had even greater resistance to fading during washing or in the sun, andcopper phthalocyanine.
The Blue Boy (1770), featuring lapis lazuli, indigo, and cobalt colourants,[28]
A synthetic indigo dye factory in Germany in 1890.
Dyes for textiles and food
[29]Woad andtrue indigo were once used but since the early 1900s, all indigo is synthetic. Produced on an industrial scale, indigo is the blue of blue jeans. Blue dyes are organic compounds, both synthetic and natural.
For food, the triarylmethane dyeBrilliant blue FCF is used for candies. The search continues for stable, natural blue dyes suitable for the food industry.[29]
Variousraspberry-flavoured foods are dyed blue. This was done to distinguishstrawberry,watermelon andraspberry-flavoured foods.[30] The companyICEE used Blue No. 1 for their blue raspberry ICEEs.
Blue Raspberry Frozen Yogurt with White Chocolate Chips, Coconut, and Cherries.
Blue haribo jelly beans. Raspberry flavour. Bought in the UK.
A blue raspberry-flavoured Jolly Rancher Hard Candy Stix after being unwrapped in the Dulles section of Sterling, Loudoun County, Virginia.
Bluepigments were once produced from minerals, especiallylapis lazuli and its close relativeultramarine. These minerals were crushed, ground into powder, and then mixed with a quick-drying binding agent, such as egg yolk (tempera painting); or with a slow-drying oil, such aslinseed oil, foroil painting. Two inorganic but synthetic blue pigments arecerulean blue (primarily cobalt(II) stanate:Co2SnO4) andPrussian blue (milori blue: primarilyFe7(CN)18). The chromophore in blueglass and glazes iscobalt(II). Diverse cobalt(II) salts such as cobalt carbonate or cobalt(II) aluminate are mixed with the silica prior to firing. The cobalt occupies sites otherwise filled with silicon.
When sunlight passes through the atmosphere, the blue wavelengths are scattered more widely by the oxygen and nitrogen molecules, and more blue comes to our eyes. This effect is calledRayleigh scattering, afterLord Rayleigh and confirmed byAlbert Einstein in 1911.[32][33]
The sea is seen as blue for largely the same reason: the water absorbs the longer wavelengths of red and reflects and scatters the blue, which comes to the eye of the viewer. The deeper the observer goes, the darker the blue becomes. In the open sea, only about 1% of light penetrates to a depth of 200 metres (seeunderwater andeuphotic depth).
The colour of the sea is also affected by the colour of the sky, reflected by particles in the water; and byalgae and plant life in the water, which can make it look green; or by sediment, which can make it look brown.[34]
The farther away an object is, the more blue it often appears to the eye. For example, mountains in the distance often appear blue. This is the effect ofatmospheric perspective; the farther an object is away from the viewer, the less contrast there is between the object and its background colour, which is usually blue. In a painting where different parts of the composition are blue, green and red, the blue will appear to be more distant, and the red closer to the viewer. The cooler a colour is, the more distant it seems.[35] Blue light isscattered more than other wavelengths by the gases in theatmosphere, hence our "blue planet".
Some of the most desirable gems are blue, includingsapphire andtanzanite. Compounds of copper(II) are characteristically blue and so are many copper-containing minerals.Azurite (Cu3(CO3)2(OH)2), with a deep blue colour, was once employed in medieval years, but it is unstable pigment, losing its colour especially under dry conditions.Lapis lazuli, mined in Afghanistan for more than three thousand years, was used for jewelry and ornaments, and later was crushed and powdered and used as a pigment. The more it was ground, the lighter the blue colour became. Naturalultramarine, made by grinding lapis lazuli into a fine powder, was the finest available blue pigment in the Middle Ages and theRenaissance. It was extremely expensive, and inItalian Renaissance art, it was often reserved for the robes of theVirgin Mary.
Intense efforts have focused on blue flowers and the possibility that natural blue colourants could be used as food dyes.[29] Commonly, blue colours in plants areanthocyanins: "the largest group of water-soluble pigments found widespread in the plant kingdom".[37] In the few plants that exploit structural colouration, brilliant colours are produced by structures within cells. The most brilliant blue colouration known in any living tissue is found in the marble berries ofPollia condensata, where a spiral structure of cellulose fibrils scattering blue light. The fruit ofquandong (Santalum acuminatum) can appear blue owing to the same effect.[29]
Blue eyes actually contain no blue pigment. The colour is caused by an effect calledTyndall scattering.
Blue eyes do not actually contain any blue pigment.Eye colour is determined by two factors: thepigmentation of the eye'siris[47][48] and thescattering of light by theturbid medium in thestroma of the iris.[49] In humans, the pigmentation of the iris varies from light brown to black. The appearance of blue, green, and hazel eyes results from theTyndall scattering of light in the stroma, an optical effect similar to what accounts for the blueness of the sky.[49][50] The irises of the eyes of people with blue eyes contain less darkmelanin than those of people with brown eyes, which means that they absorb less short-wavelength blue light, which is instead reflected out to the viewer. Eye colour also varies depending on the lighting conditions, especially for lighter-coloured eyes.
In the United States, as of 2006, 1 out of every 6 people, or 16.6% of the total population, and 22.3% of thewhite population, have blue eyes, compared with about half of Americans born in 1900, and a third of Americans born in 1950. Blue eyes are becoming less common among American children[citation needed]. In the US, males are 3–5% more likely to have blue eyes than females.[51]
A term for Blue was relatively rare in many forms of ancient art and decoration, and even in ancient literature. The Ancient Greek poets described the sea as green, brown or "the colour of wine". The colour is mentioned several times in theHebrew Bible as 'tekhelet'. Reds, blacks, browns, and ochres are found incave paintings from the UpperPaleolithic period, but not blue. Blue was also not used for dyeing fabric until long after red, ochre, pink, and purple. This is probably due to the perennial difficulty of making blue dyes and pigments. On the other hand, the rarity of blue pigment made it even more valuable.[62]
The earliest known blue dyes were made from plants –woad in Europe,indigo in Asia and Africa, while blue pigments were made from minerals, usually eitherlapis lazuli orazurite, and required more.[63] Blue glazes posed still another challenge since the early blue dyes and pigments were not thermally robust. Inc. 2500 BC, the blue glazeEgyptian blue was introduced for ceramics, as well as many other objects.[64][65] The Greeks imported indigo dye from India, calling it indikon, and they painted with Egyptian blue. Blue was not one of the four primary colours for Greek painting described byPliny the Elder (red, yellow, black, and white). For the Romans, blue was the colour of mourning, as well as the colour of barbarians. The Celts and Germans reportedly dyed their faces blue to frighten their enemies, and tinted their hair blue when they grew old.[66] The Romans made extensive use of indigo and Egyptian blue pigment, as evidenced, in part, by frescos inPompeii.The Romans had many words for varieties of blue, includingcaeruleus,caesius,glaucus,cyaneus,lividus,venetus,aerius, andferreus, but two words, both of foreign origin, became the most enduring;blavus, from the Germanic wordblau, which eventually becamebleu or blue; andazureus, from the Arabic wordlazaward, which became azure.[67]
Blue was widely used in the decoration of churches in the Byzantine Empire.[68] By contrast, in the Islamic world, blue was of secondary to green, believed to be the favourite colour of theProphet Mohammed. At certain times inMoorish Spain and other parts of the Islamic world, blue was the colour worn by Christians and Jews, because only Muslims were allowed to wear white and green.[69]
In the art and life of Europe during the earlyMiddle Ages, blue played a minor role. This changed dramatically between 1130 and 1140 in Paris, when theAbbe Suger rebuilt theSaint Denis Basilica. Suger considered that light was the visible manifestation of the Holy Spirit.[70] He installedstained glass windows coloured withcobalt, which, combined with the light from the red glass, filled the church with a bluish violet light. The church became the marvel of theChristian world, and the colour became known as the"bleu de Saint-Denis". In the years that followed even more elegant blue stained glass windows were installed in other churches, including atChartres Cathedral andSainte-Chapelle in Paris.[71]
In the 12th century the Roman Catholic Church dictated that painters in Italy (and the rest of Europe consequently) to paint the Virgin Mary with blue, which became associated with holiness, humility and virtue. In medieval paintings, blue was used to attract the attention of the viewer to the Virgin Mary. Paintings of the mythicalKing Arthur began to show him dressed in blue. The coat of arms of the kings of France became an azure or light blue shield, sprinkled with goldenfleur-de-lis or lilies. Blue had come from obscurity to become the royal colour.[72]
Renaissance through 18th century
Blue came into wider use beginning in the Renaissance, when artists began to paint the world with perspective, depth, shadows, and light from a single source. In Renaissance paintings, artists tried to create harmonies between blue and red, lightening the blue with lead white paint and adding shadows and highlights.Raphael was a master of this technique, carefully balancing the reds and the blues so no one colour dominated the picture.[73]
Ultramarine was the most prestigious blue of the Renaissance, being more expensive than gold. Wealthy art patrons commissioned works with the most expensive blues possible. In 1616Richard Sackville commissioned a portrait of himself byIsaac Oliver with three different blues, including ultramarine pigment for his stockings.[74]
Portrait of Richard Sackville (1616), using three expensive blues, including ultramarine for his stockings
Ming dynasty, Porcelain vase painted with cobalt blue under transparent glaze. (15th c.) (Metropolitan Museum)
Delftware plaque with cobalt blue painting (1683) (Rijksmuseum, Amsterdam)
An industry for the manufacture of fine blue and white pottery began in the 14th century inJingdezhen, China, using white Chinese porcelain decorated with patterns ofcobalt blue, imported from Persia. It was first made for the family of the Emperor of China, then was exported around the world, with designs for export adapted to European subjects and tastes. The Chinese blue style was also adapted by Dutch craftsmen inDelft and English craftsmen inStaffordshire in the 17th-18th centuries. in the 18th century, blue and white porcelains were produced byJosiah Wedgwood and other British craftsmen.[75]
19th-20th century
Beau Brummel (1776–1840) introduced the ancestor of the modern blue suit
The early 19th century saw the ancestor of the modern blue business suit, created byBeau Brummel (1776–1840), who set fashion at the London Court. It also saw the invention ofblue jeans, a highly popular form of workers's costume, invented in 1853 byJacob W. Davis who used metal rivets to strengthen bluedenim work clothing in the California gold fields. The invention was funded by San Francisco entrepreneurLevi Strauss, and spread around the world.[76]
Van Gogh'sStarry Night Over the Rhône (1888). Blue used to create a mood or atmosphere. A cobalt blue sky, and cobalt or ultramarine water.
Recognizing the emotional power of blue, many artists made it the central element of paintings in the 19th and 20th centuries. They includedPablo Picasso,Pavel Kuznetsov and theBlue Rose art group, andKandinsky andDer Blaue Reiter (The Blue Rider) school.[77]Henri Matisse expressed deep emotions with blue, "A certain blue penetrates your soul."[78] In the second half of the 20th century, painters of theabstract expressionist movement use blues to inspire ideas and emotions. PainterMark Rothko observed that colour was "only an instrument;" his interest was "in expressing human emotions tragedy, ecstasy, doom, and so on".[79]
In the 17th century. The Prince-Elector of Brandenburg,Frederick William I of Prussia, chosePrussian blue as the new colour of Prussian military uniforms, because it was made withWoad, a local crop, rather thanIndigo, which was produced by the colonies of Brandenburg's rival, England. It was worn by the German army until World War I, with the exception of the soldiers of Bavaria, who wore sky-blue.[80]
In 1748, theRoyal Navy adopted a dark shade of blue for the uniform of officers.[76] It was first known as marine blue, now known asnavy blue.[81] The militia organized byGeorge Washington selected blue andbuff, the colours of the BritishWhig Party. Blue continued to be the colour of the field uniform of the US Army until 1902, and is still the colour of the dress uniform.[82]
In the 19th century, police in the United Kingdom, including theMetropolitan Police and theCity of London Police also adopted a navy blue uniform. Similar traditions were embraced in France and Austria.[83] It was also adopted at about the same time for the uniforms of the officers of theNew York City Police Department.[76]
Blue is used to representmales. Beginning as a trend the mid-19th century and applying primarily to clothing, gendered associations with blue became more widespread from the 1950s. The colour became associated with males afterWorld War II.[84]
This restroom sign on anAll Nippon Airways Boeing 767-300 uses pink for the female gender and blue for the male gender.
Blue in Judaism: In theTorah,[85] theIsraelites were commanded to put fringes,tzitzit, on the corners of their garments, and to weave within these fringes a "twisted thread of blue (tekhelet)".[86] In ancient days, this blue thread was made from a dye extracted from a Mediterranean snail called thehilazon.Maimonides claimed that this blue was the colour of "the clear noonday sky";Rashi, the colour of the evening sky.[87] According to several rabbinic sages, blue is the colour of God's Glory.[88] Staring at this colour aids in mediation, bringing us a glimpse of the "pavement of sapphire, like the very sky for purity", which is a likeness of the Throne of God.[89] (TheHebrew word for glory) Many items in theMishkan, the portable sanctuary in the wilderness, such as themenorah, many of the vessels, and theArk of the Covenant, were covered with blue cloth when transported from place to place.[90]
Blue inChristianity: Blue is particularly associated with theVirgin Mary. This was the result of a decree ofPope Gregory I (540–601) who ordered that all religious paintings should tell a story which was clearly comprehensible to all viewers, and that figures should be easily recognizable, especially that of the figure of Mary. If she was alone in the image, her costume was usually painted with the finest blue,ultramarine. If she was with Christ, her costume was usually painted with a less expensive pigment, to avoid outshining him.[91][92][93][94]
Blue inHinduism: Many of the gods are depicted as having blue-coloured skin, particularly those associated withVishnu, who is said to be the preserver of the world, and thus intimately connected to water.Krishna andRama, Vishnu's avatars, are usually depicted with blue skin.Shiva, the destroyer deity, is also depicted in a light-blue hue, and is calledNīlakaṇṭha, or blue-throated, for having swallowed poison to save the universe during theSamudra Manthana, the churning of the ocean of milk. Blue is used to symbolically represent the fifth, and the throat,chakra (Vishuddha).[95]
Blue inPaganism: Blue is associated with peace, truth, wisdom, protection, and patience. It helps with healing, psychic ability, harmony, and understanding.[98]
Flag of theEuropean Union is "reflex blue", a medium dark blue
A presidential-election map of the US, 2008–2020. States that consistently vote for Democrats are termed "blue states".
Unlike red or green, blue was not strongly associated with any particular country, religion or political movement. As the colour of harmony, it was chosen as the colour for the flags of theUnited Nations, theEuropean Union, andNATO.[101] In politics, blue is often used as the colour of conservative parties, contrasting with the red associated with left-wing parties.[102] Some conservative parties that use the colour blue include theConservative Party (UK),[103]Conservative Party of Canada,[104]Liberal Party of Australia,[105]Liberal Party of Brazil, andLikud of Israel.[citation needed] However, in some countries, blue is not associated main conservative party. In the United States, the liberalDemocratic Party is associated with blue, while the conservativeRepublican Party with red. US states which have been won by the Democratic Party in four consecutive presidential elections are termed "blue states", while those that have been won by the Republican Party are termed "red states".[106]South Korea also uses this colour model, with theDemocratic Party on the left using blue[107] and thePeople Power Party on the right using red.
^"Iridescence in Lepidoptera".Natural Photonics (originally in Physics Review Magazine). University of Exeter. September 1998. Archived fromthe original on 7 April 2014. Retrieved27 April 2012.
^Michel Pastoureau,Bleu – Histoire d'une couleur, pp. 114–16
^Roger Keyes,Japanese Woodblock Prints: A Catalogue of the Mary A. Ainsworth Collection, R, Allen Memorial Art Museum, Oberlin College, 1984, p. 42, plate #140, p. 91 and catalogue entry #439, p. 185. for more on the story of Prussian blue in Japanese prints, see also the website of the Victoria and Albert Museum, London.
^Maerz and Paul (1930).A Dictionary of Color New York: McGraw Hill p. 206
^abcdNewsome, Andrew G.; Culver, Catherine A.; Van Breemen, Richard B. (2014). "Nature's Palette: The Search for Natural Blue Colorants".Journal of Agricultural and Food Chemistry.62 (28):6498–6511.Bibcode:2014JAFC...62.6498N.doi:10.1021/jf501419q.PMID24930897.
^Glenn S. Smith (July 2005)."Human color vision and the unsaturated blue color of the daytime sky"(PDF).American Journal of Physics.73 (7):590–597.Bibcode:2005AmJPh..73..590S.doi:10.1119/1.1858479.Archived(PDF) from the original on 15 July 2011.Near sunrise and sunset, most of the light we see comes in nearly tangent to the Earth's surface, so that the light's path through the atmosphere is so long that much of the blue and even green light is scattered out, leaving the sun rays and the clouds it illuminates red. Therefore, when looking at the sunset and sunrise, the colour red is more perceptible than any of the other colours.
^Harmon, A. D.; Weisgraber, K. H.; Weiss, U. (1980). "Preformed azulene pigments ofLactarius indigo (Schw.) Fries (Russulaceae, Basidiomycetes)".Experientia.36:54–56.doi:10.1007/BF02003967.S2CID21207966.
^Nuno Mateas, Victor de Freitas (2008). "Anthrocyanins as Food Colorants". In Gould, K.; Davies, K.; Winefield, C. (eds.).Anthocyanins: Biosynthesis, Functions, and Applications. Springer. p. 283.ISBN978-0-387-77334-6.
^DIKSHIT, K.N. (2012). "The Rise of Indian Civilization: Recent Archaeological Evidence from the Plains of 'Lost' River Saraswati and Radio-Metric Dates".Bulletin of the Deccan College Research Institute. 72/73:1–42.ISSN0045-9801.JSTOR43610686.
^Chase, W.T. 1971, "Egyptian blue as a pigment and ceramic material." In: R. Brill (ed.)Science and Archaeology. Cambridge, Mass: MIT Press.ISBN0-262-02061-0
^J. Baines, "Color Terminology and Color Classification in Ancient Egyptian Color Terminology and Polychromy", inThe American Anthropologist, volume 87, 1985, pp. 282–97.
^Caesar,The Gallic Wars, V., 14, 2. Cited by Miche Pastourou, p. 178.
^Jean Tulard, Jean-François Fayard, Alfred Fierro,Histoire et dictionnaire de la Révolution française, 1789–1799, Éditions Robert Laffont, collection Bouquins, Paris, 1987.ISBN2-7028-2076-X
^"더불어민주당". 8 March 2023. Archived fromthe original on 8 March 2023. Retrieved13 February 2024.
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![Prussian blue, FeIII 4[FeII (CN) 6] 3, is the blue of blueprints.](/mt/?noimg=&dark=on&url=http%3a%2f%2fwww.wikipedia.org%2fwiki%2fFile%3aPrussian_blue.jpg)
![The Blue Boy (1770), featuring lapis lazuli, indigo, and cobalt colourants,[28]](/mt/?noimg=&dark=on&url=http%3a%2f%2fwww.wikipedia.org%2fwiki%2fFile%3aThe_Blue_Boy.jpg)
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