From the Renaissance onward, painters used this system to create their colours. Mixing all three primary colours together produces a dark grey. Red and blue mixed together form violet, blue and yellow together form green. In painting and traditional colour theory, blue is one of the three primary colours of pigments (red, yellow, blue), which can be mixed to form a wide gamut of colours. He included indigo, the hue between blue and violet, as one of the separate colours, though today it is usually considered a hue of blue. He chose seven colours because that was the number of notes in the musical scale, which he believed was related to the optical spectrum. Isaac Newton included blue as one of the seven colours in his first description the visible spectrum. Pure blue, in the middle, has a wavelength of 470 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. Human eyes perceive blue when observing light which has a dominant wavelength of roughly 450вЂ“495 nanometres. Colour names often developed individually in natural languages, typically beginning with black and white (or dark and light), and then adding red, and only much later вЂ“ usually as the last main category of colour accepted in a language вЂ“ adding the colour blue, probably when blue pigments could be manufactured reliably in the culture using that language. Linguistic research indicates that languages do not begin by having a word for the colour blue.

(For more on this subject, see Distinguishing blue from green in language) In Lakota, the word tИџГі is used for both blue and green, the two colours not being distinguished in older Lakota. In Japanese, the word for blue ( йќ’ ao) is often used for colours that English speakers would refer to as green, such as the colour of a traffic signal meaning 'go'. For example, in Vietnamese, the colour of both tree leaves and the sky is xanh. Several languages, including Japanese, and Lakota Sioux, use the same word to describe blue and green. In Russian, Spanish and some other languages, there is no single word for blue, but rather different words for light blue (РіРѕР»СѓР±РѕР№, goluboj Celeste) and dark blue (СЃРёРЅРёР№, sinij Azul). In heraldry, the word azure is used for blue. 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 (meaning shimmering, lustrous). The same surveys also showed that blue was the colour most associated with the masculine, just ahead of black, and was also the colour most associated with intelligence, knowledge, calm, and concentration. In US and European public opinion polls it is the most popular colour, chosen by almost half of both men and women as their favourite colour. 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 occasionally with sadness. Distant objects appear more blue because of another optical effect called aerial perspective. An optical effect called Tyndall effect explains blue eyes. The clear daytime sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering. Most blues contain a slight mixture of other colours azure contains some green, while ultramarine contains some violet. The eye perceives blue when observing light with a dominant wavelength between approximately 450 and 495 nanometres. It lies between violet and cyan on the spectrum of visible light. Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model.

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