blue & red
Wiki, Facts

 blue & red facts

• Human eyes perceive blue when observing light with a wavelength between 450 and 495 nanometres, which is between 45 and 49
• 5 Ångströms
• 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 nanometers (47 Ångströms)
• 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 Old Dutch, Old High German, Old Saxon blāo and Old Frisian blāw, blau
• 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