    [[Blueberries]] ''[[Lactarius indigo'' is one of only a few blue-coloured mushrooms.]] Blue Turkish Tiles sky and water are often blue.]] '''Blue''' is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal mixture of red and green light. On a colour wheel based on traditional colour theory (RYB) where blue was considered a primary colour, its complementary colour is considered to be orange (based on the Munsell colour wheel).   The English language commonly uses &quot;blue&quot; to refer to any colour from navy blue to cyan. The word itself is derived from the Old French word ''bleu''.  ==Etymology and definitions==  The modern English word ''blue'' comes from Middle English ''bleu'' or ''blewe'', from Old French ''bleu'', ''bleve'', ''blöe'', a word of Germanic origin (Frankish or possibly Old High German ''blāo'', &quot;blue&quot;). ''Bleu'' replaced Old English ''blāw'' &quot;blue&quot; and ''blǣwen'' &quot;light blue&quot;. The root of all these variations is Proto-Germanic ''blǣwaz'', from Proto-Indo-European *''bhlāw-, *bhlēw-'' &quot;light-coloured, yellow, grey, blue&quot;, from *''bhel-'' &quot;to shine, be light or bright&quot;, also the root of Old Norse ''blār'' and the modern Icelandic ''blár'', and the Scandinavian word ''blå'', which can also refer to other non blue colours.  A Scots and Scottish English word for &quot;blue-grey&quot; is ''blae'', from the Middle English ''bla'' (&quot;dark blue&quot;, from Old Norse ''blār''). Also related is the English word ''blee'' meaning &quot;colour, complexion&quot;. Ancient Greek lacked a word for blue and Homer called the colour of the sea &quot;wine dark&quot;, except that the word ''kyanos'' (cyan) was used for dark blue enamel. As a curiosity, ''blue'' is thought to be cognate with ''black'', ''blond'', and bleach, in the sense of ''blank'', and through the Germanic word. Through a Proto-Indo-European root, it is also linked with Latin ''flavus'' (&quot;yellow&quot;; see ''flavescent'' and ''flavine''), with Greek ''phalos'' (white), French ''blanc'' (white, blank) (borrowed from Old Frankish), and with Russian белый, ''belyi'' (&quot;white,&quot; see ''beluga''), and Welsh ''blawr'' (grey) all of which derive (according to the ''American Heritage Dictionary'') from the Proto-Indo-European root ''*bhel-'' meaning &quot;to shine, flash or burn&quot;, (more specifically the word bhle-was, which meant light coloured, blue, blond, or yellow), whence came the names of various bright colours, and that of colour black from a derivation meaning &quot;burnt&quot; (other words derived from the root ''*bhel-'' include ''bleach, ''bleak'', ''blind'', ''blink'', ''blank'', ''blush'', ''blaze'', ''flame'', ''fulminate'', ''flagrant'' and ''phlegm'').  In the English language, blue may refer to the feeling of sadness. &quot;He was feeling blue&quot;. This is because blue was related to rain, or storms, and in Greek mythology, the god Zeus would make rain when he was sad (crying), and a storm when he was angry. ''Kyanos'' was a name used in Ancient Greek to refer to ''dark blue tile'' (in English it means blue-green or cyan).''Merriam-Webster's Ninth New Collegiate Dictionary'' Springfield, Mass.:1984--Merriam-Webster Page 319 The phrase &quot;feeling blue&quot; is linked also to a custom among many old deepwater sailing ships. If the ship lost the captain or any of the officers during its voyage, she would fly blue flags and have a blue band painted along her entire hull when returning to home port.[  &quot;US Navy - origins of Navy Terminology&quot;]  Many languages do not have separate terms for blue and or green, instead using a cover term for both (when the issue is discussed in linguistics, this cover term is sometimes called ''grue'' in English).  ==In science== ===Pigments and dyes=== Traditionally, blue has been considered a primary colour in painting, with the secondary colour orange as its complement.  Blue pigments include azurite (, ultramarine (), cerulean blue (primarily cobalt (II) stanate: ), cobalt blue (cobalt(II) aluminate: ), and Prussian blue (milori blue: primarily ).  Traditionally natural dyes such as woad and true indigo were used to produce indigo dye used to colour fabrics blue or indigo. These have now largely been replaced by synthetic dyes.  ===Scientific natural standards for blue=== * Emission spectrum of  * Electronic spectrum of aqua-ions   ===Animals=== ''[[Dendrobates azureus'']] [[Blue Jay]] *When an animal's coat is described as &quot;blue&quot;, it usually refers to a shade of grey that takes on a bluish tint, a diluted variant of a pure black coat. This designation is used for a variety of animals, including dog coats, some rat coats, cat coats, some chicken breeds, some horse coat colours and rabbit coat colours. Some animals, such as giraffes and lizards, also have blue tongues.  ==In culture== ===Symbolic language=== * In the English language, blue often represents the human emotion of sadness, for example, &quot;He was feeling blue&quot;. In German, on the other hand, to be &quot;blue&quot; (''blau sein'') is to be drunk. This derives from the ancient use of urine (which is produced copiously by the human body after drinking alcohol) in dyeing cloth blue with woad or indigo.Heller, Eva.  ''Wie Farben wirken: Farbpsychologie, Farbsymbolik, kreative Farbgestaltung''.  Berlin: Rowohlt, 2004. It may also be in relation to rain, which is usually regarded as a trigger of depressive emotions.[ Top 10 weather complaints]  *Conversely blue, a very popular colour[ Preferences - Favorite Color] can represent happiness and optimism[ Psychology of Color] as days with clearer, blue skies tend to be considered times where these emotions are more easily expressed. Many artistic contributions have been made referencing clear days with blue skies as part of the happiness or as a symbolism of the happiness the artist felt, such as Tony Bennett's Put on a Happy Face.[ &quot;Put on a Happy Face&quot; lyrics] If this were untrue there would obviously be more complaints about days with clear blue skies.  *Blue is commonly used in the Western hemisphere to symbolize the male gender in contrast to pink used for females, although in the early 1900s, blue was the colour for girls (as it had traditionally been the colour of the Virgin Mary in Western Art) and pink was for boys (as it was akin to the colour red, considered a masculine colour.  ===National colours=== [[Flag of Greece]] [[Coat of Arms symbol of Israel]]  * ''Azzurro'', a light blue, is the national colour of Italy (from the livery colour of the former reigning family, the House of Savoy). * Blue is the national sports colour for India, as it denotes secularism. * Blue is the national colour used on flags of several countries surrounded by seas or oceans such as Australia and Europe, though not necessarily with this interpretation in mind. * Blue and white are the national colours of Scotland, Argentina, El Salvador, Finland, Greece, Guatemala, Honduras, Israel, Micronesia, Nicaragua, and Somalia as well as of the United Nations using a light shade of blue symbolising peace. * Blue and yellow are the national colours of Barbados, Kazakhstan, Palau, Sweden, and Ukraine, and along with green, of Brazil, and along with red, of Chad, Colombia, Ecuador, Moldova, Romania, and Venezuela. * Blue, white and yellow are the national colours of Bosnia and Herzegovina, Kosovo and Uruguay. * Blue and red are the national colours of Haiti and Liechtenstein, and (along with white) of Cambodia, Costa Rica, Chile, Croatia, Cuba, the Czech Republic, the Dominican Republic, France, Iceland, North Korea, Laos, Liberia, Luxembourg, Myanmar, Nepal, the Netherlands, New Zealand, Norway, Panama, Paraguay, Russia, Samoa, Serbia, Slovakia, Slovenia, Thailand, the United Kingdom, and the United States * Blue, white and black are the national colours of Estonia.&quot;Estonia in brief: National Symbols&quot; at Estonica website [ Estonica.org]  ===Mysticism=== * In Hinduism, Blue is used to symbolically represent the fifth, throat chakra (Vishuddha).Stevens, Samantha. The Seven Rays: a Universal Guide to the Archangels. City: Insomniac Press, 2004. ISBN 1-894663-49-7 pg. 24  ===Politics===   * The Blue House is the residence of the President of South Korea. * Blue has been associated with a variety of political positions, often differentiated from communist red or anarchist black. During the revolt in the Vendée against the French Revolution, blues stood for the revolutionary forces, and white for the counter-revolutionaries. Later movements like the Breton blues used the colour to signify allegiance to the ideals of the revolution. * The blueshirts was a quasi-fascist political organisation active in Ireland during the 1930s (the name comes from the fact that St. Patrick's Blue is one of the traditional colours of Ireland). * Blue is the colour of the Conservative Party in Britain and Conservative Party of Canada. Television coverage in the United States since the 2000 presidential election has made it fashionable to link the Democratic Party to &quot;blue&quot; and the Republican Party to &quot;red&quot; (especially in reference to &quot;red states and blue states&quot;). In Brazil, blue states are the ones in which the Social Democratic Party has the majority, in opposition to the Workers' Party, usually represented by red. Blue stripes on a traditional Jewish [[tallit.]] * A blue law is a type of law, typically found in the United States and Canada, designed to enforce religious standards, particularly the observance of Sunday as a day of worship or rest, and a restriction on Sunday shopping. The word ''blue'' was used in the 17th century as a disparaging reference to rigid moral codes and those who observed them, particularly in ''blue-stocking'', a reference to Oliver Cromwell's supporters in the parliament of 1653. * Blue is associated with numerous centre-right liberal political parties in Europe, Including the People's Party for Freedom and Democracy (Netherlands), the Reformist Movement and Open VLD (Belgium), the Democratic Party (Luxembourg), Liberal Party (Denmark) and Liberal People's Party (Sweden).  ===Religion=== * Blue is associated in Christianity generally and Catholicism in particular, with the Virgin Mary. * Blue in Hinduism: Many of the gods are depicted as having blue-coloured skin, particularly those associated with Vishnu, who is said to be the Preserver of the world and thus intimately connected to water. Krishna and Ram, Vishnu's avatars, are usually blue. Shiva, the Destroyer, is also depicted in light blue tones and is called ''neela kantha'', or blue-throated, for having swallowed poison in an attempt to turn the tide of a battle between the gods and demons in the gods' favour. * Blue in Judaism: In the Torah,Numbers 15:38. the Israelites were commanded to put fringes, ''tzitzit'', on the corners of their garments, and to weave within these fringes a &quot;twisted thread of blue (''tekhelet'')&quot;.[ Tekhelet.com], the Ptil Tekhelet Organization In ancient days, this blue thread was made from a dye extracted from a Mediterranean snail called the ''hilazon''. Maimonides claimed that this blue was the colour of &quot;the clear noonday sky&quot;; Rashi, the colour of the evening sky.''Mishneh Torah'', ''Tzitzit'' 2:1; Commentary on Numbers 15:38. According to several rabbinic sages, blue is the colour of God's Glory.''Numbers Rabbah'' 14:3; ''Hullin'' 89a. Staring at this colour aids in mediation, bringing us a glimpse of the &quot;pavement of sapphire, like the very sky for purity&quot;, which is a likeness of the Throne of God.Exodus 24:10; Ezekiel 1:26; ''Hullin'' 89a. (The Hebrew word for glory.) Many items in the ''Mishkan'', the portable sanctuary in the wilderness, such as the ''menorah'', many of the vessels, and the Ark of the Covenant, were covered with blue cloth when transported from place to place.Numbers 4:6-12. * Blue in Islam: In verse 20:102 of the Qur’an, the word زرق ''zurq'' (plural of ''azraq'' 'blue') is used metaphorically for evildoers whose eyes are glazed with fear, as if the sclera is filmed over with a bluish tint.  ===Symbolism=== * In Thailand, blue is associated with Friday on the Thai solar calendar. Anyone may wear blue on Fridays and anyone born on a Friday may adopt blue as their colour. The Thai language, however, is one that has had trouble distinguishing blue from green. The default word for Blue was recently สีน้ำเงิน literally, the colour of silver, a poetical reference to the silvery sheen of the deep blue sea. It now means navy blue, and the default word is now สีฟ้า literally, the colour of the sky.    ==Variations==   