Blue

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 colours.

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 colourless, 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.

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

Usage, symbolism, colloquial expressions

• 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 People's Republic of China changed the colour 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 colour 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.
• 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 endeavours.
• 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.
• 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.
• Blue is associated with manhood, as pink is associated with womanhood.
• Nationally
  • In Australia, a "blue" can also describe a fight or an argument. Men with red hair may be nicknamed "Bluey".
  • The German word for blue is used for "drunk".
  • In Russian, the word for light blue is slang for "gay".
  • Blue movie is a slang term for a pornographic film. There are also "blue magazines". This term is more common in Britain than the United States. Also used in Israel.
• 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 colours 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 colour of Italy.
• "Big Blue" is a nickname for IBM.
• A blue moon is the second full moon in a calendar month, the third full moon in a season that has four, or a moon that appears blue because of particles in the atmosphere. All 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 for a solid "blue" coat or Australian Shepherd for blue
  

House painted blue

Colors | List of colors

White Silver Gray Black

Red Orange Yellow Green Blue Indigo Violet

Pink Chartreuse Teal Cyan Azure Magenta

Aquamarine Beige Bistre Brown Cardinal Carmine Coral Crimson Emerald Gold Lavender Maroon Mauve

Navy blue Ochre Olive Peach Powder blue Purple Salmon Tan

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