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Blue is the colour between violet and green on the optical spectrum of visible light. Human eyes perceive blue when observing light with a wavelength between 450 and 495 nanometres. 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. Pure blue, in the middle, has a wavelength of 470 nanometres. In painting and traditional colour theory, blue is one of the three primary colours of pigments, along with red and yellow, which can be mixed to form a wide gamut of colours. Red and blue mixed together form violet, blue and yellow together form green. Blue is also a primary colour in the RGB colour model, used to create all the colours on the screen of a television or computer monitor. The modern English word ''blue'' comes from Middle English ''bleu'' or ''blewe'', from the Old French ''bleu'', a word of Germanic origin, related to the Old High German word ''blao''.〔''Webster's Seventh New Collegiate Dictionary'', (1970).〕 The clear sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering. 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. Rayleigh scattering also explains blue eyes; there is no blue pigment in blue eyes. Distant objects appear more blue because of another optical effect called atmospheric perspective. Blue has been used for art, decoration and as a clothing dye since ancient times. The semi-precious stone lapis lazuli, coming from mines in Afghanistan, was used in ancient Egypt for jewelry and ornament and later, in The Renaissance, to make the pigment ultramarine, the most expensive of all pigments. In the Middle Ages, cobalt blue was used to colour the stained glass windows of cathedrals. Beginning in the 9th century, Chinese artists used cobalt to make fine blue and white porcelain. Blue dyes for clothing were made from woad in Europe and indigo in Asia and Africa. In 1828 a synthetic ultramarine pigment was developed, and synthetic blue dyes and pigments gradually replaced mineral pigments and vegetable dyes. Pierre-Auguste Renoir, Vincent van Gogh and other late 19th century painters used ultramarine and cobalt blue not just to depict nature, but to create moods and emotions. In the late 18th century and 19th century, blue became a popular colour for military uniforms and police uniforms. In the 20th century, because blue was commonly associated with harmony, it was chosen as the colour of the flags of the United Nations and the European Union. Toward the end of the 20th century, dark blue replaced black and grey as the most common colour for business suits, because it was seen as serious without being grim. Surveys in the US and Europe show that blue is the colour most commonly associated with harmony, faithfulness, confidence, distance, infinity, the imagination, cold, and sometimes with sadness.〔Eva Heller (2009), ''Psychologie de la Couleur'', pg. 13.〕 In US and European public opinion polls it is overwhelmingly the most popular colour, chosen by almost half of both men and women as their favourite colour.〔 ==Shades and variations== (詳細はvisible spectrum. Hues of blue include indigo and ultramarine, closer to violet; pure blue, without any mixture of other colours; Cyan, which is midway on the spectrum between blue and green, and the other blue-greens turquoise, teal, and aquamarine. Blues also vary 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, and Prussian blue; while lighter tints include sky blue, azure, and Egyptian blue. (For a more complete list see the List of colours). Blue pigments were originally made from minerals such as lapis lazuli, cobalt and azurite, and blue dyes were made from plants; usually woad in Europe, and ''Indigofera tinctoria'', or true indigo, in Asia and Africa. Today most blue pigments and dyes are made by a chemical process. File:Solid blue.svg|Pure blue, also known as high blue, is not mixed with any other colours. File:000080 Navy Blue Square.svg|Navy blue, also known as low blue, is the darkest shade of pure blue. File:Gabbiano cielo.jpg|Sky blue or pale azure, mid-way on the RBG colour wheel between blue and cyan. File:Indigo plant extract sample.jpg|Extract of natural indigo, the most popular blue dye before the invention of synthetic dyes. It was the colour of the first blue jeans. File:Lapis lazuli block.jpg|A block of lapis lazuli, originally used to make ultramarine. File:Ultramarineblue.jpg|Ultramarine, the most expensive blue during the Renaissance, is a slightly violet-blue. File:Cobalt blue flask.jpg|Cobalt has been used since 2000 BC to colour cobalt glass, Chinese porcelain, and the stained glass windows of medieval cathedrals. File:Cobaltblue.jpg|The synthetic pigment cobalt blue was invented in 1802, and was popular with Vincent van Gogh and other impressionist painters. File:Cyan-square.gif|Cyan is made by mixing equal amounts of blue and green light, or removing red from white light. File:Common Teal (Anas crecca) near Hodal, Haryana W IMG 6512.jpg|The colour teal takes its name from the colour around the eyes of the common teal duck. File:Tripodic goblet Louvre AO4079.jpg|Egyptian blue goblet from Mesopotamia, 1500–1300 BC. This was the first synthetic blue, first made in about 2500 BC. File:Prussian blue.jpg|Prussian blue, invented in 1707, was the first modern synthetic blue. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「blue」の詳細全文を読む スポンサード リンク
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