Blue (from Old High German "blao" shining) is one of the three primary additive colors; blue light has the shortest wavelength (about 470 nm) of the three primary colors.

A clear sky on a sunny day is colored blue because of Rayleigh scattering of the light from the Sun. Large amounts of water (H₂O) look blue because red light around 750 nm is absorbed as an overtone of the O-H stretching vibration. Interestingly, heavy water (D₂O) is colorless, because the absorption band is at a longer wavelength (~950 nm).

An example of a blue color in the RGB color space has intensities [0, 0, 255] on a 0 to 255 scale. Blue is the complement of yellow; blue pigments absorb yellow light.

On a browser that supports visual formatting in Cascading Style Sheets, the following box should appear in this color:

The English language commonly uses "blue" to refer to any color from blue to cyan.

Usage, symbolism, colloquial expressions

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• The colloquial expression "blue" is used to describe melancholy or sadness in English speaking countries. See also Blues music.
• The word "blue" is often used in reference to the Police force; e.g. "Boys in Blue", "the blue line"
• Blue is also the color of many police uniforms. Police in the Peoples Republic of China changed the color of the uniforms from green to blue in the late 1990s partly to emphasize their civilian role.
• Blue is the color of many air force dress uniforms.
• Blue is used to denote the working class (due to the usual color of working clothes). Blue-collar workers are industrial workers as opposed to white-collar office workers.
• The phrase "of blue blood" is used to mean "from an aristocratic background", because a pale, untanned skin allows blue-tinged veins to show through.
• Blue movie is a slang term for a pornographic film. There are also "blue magazines". This term is more common in Great Britain than the United States.
• Users of Microsoft Windows often use the term "blue" to describe a computer that has encountered a blue screen of death.
• "Blue laws" is a slang term for laws regulating issues of morality, such as alcohol, gambling, or sexually-explicit materials.
• The Blue Riband is a prize awarded since the 1860s to the ship that made the fastest transatlantic crossing.
• "Blue ribbon" is a term used to describe something of high quality, such as a blue ribbon panel or a blue ribbon commission. This usage comes from the practice of awarding blue ribbons for first place in certain athletic or other competitive endeavors.
• Dark blue is associated with Oxford University and light blue with Cambridge University. Participants in sporting fixtures between these universities are said to have been awarded "a blue", similar in concept to a varsity letter.
• In Australia, a "blue" can also describe a fight or an argument.
• The German word for blue is used for "drunk".
• In Japanese, the word for blue/green is used for "young".
• In Russian, the word for blue is slang for "gay".
• Blue often denoted injury since it is the color of a bruise.
• In medical diagrams, blue is used to represent veins carrying deoxygenated blood back to the heart. Deoxygenated blood is actually reddish violet.
• Politically:
  • Electoral maps in the United States usually use blue for the Democratic Party.
  • Those in the United Kingdom and Canada use blue for the Conservative Party and Conservative Party of Canada, respectively (which use blue as one of their symbols).
  • In Germany, blue and yellow are the colors of the liberal party (FDP).
  • In the Republic of China on Taiwan, the blue is the symbol for the Kuomintang and has been used as the emblem for Chinese reunification leaning parties.
  • Internationally, blue is the color for conservatives (with notable exceptions; see Political party).

• Blue is used to represent the Union in the American Civil War in opposition to the Confederate gray, both based on the uniforms worn by the respective armies.
• Azzurro (a light blue) is the national color of Italy.
• "Big Blue" is a nickname for IBM.
• A blue moon is the second full moon in a calendar month, or a moon that appears blue because of particles in the atmosphere. Both are uncommon enough that "once in a blue moon" means "almost never."
• A blue note is a note between the regular notes on the scale. Blue notes are the most important notes in the blues scale.
• A blue dog has a coat color that is primarily gray or silver. For example, see Kerry Blue Terrier.

Music

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'Blue' is the title of an album by the Canadian singer/songwriter Joni Mitchell.

'Kind of Blue' is the title of an album by Miles Davis, which has become one of the biggest selling jazz recordings in history.

'Blue Train' is the title of an influential jazz album by John Coltrane

'Rhapsody in Blue' is a symphonic jazz composition for jazz band, piano, and orchestra by George Gershwin.

'Love is Blue' is a popular tune from the 1960's by Andy Williams, most notably performed by Paul Mauriat.

Blue is also a title for songs from LeAnn Rimes to Eiffel 65.

Color Coordinates

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See also

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• Blues
• Trois Coleurs: Bleu
• Derek Jarman's Blue
• ''Blue (1968 movie)
• Blue (1992 movie)
• Blue (2001 movie)
• Blue (2002 movie)''
• list of terms associated with the color blue

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