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Color coordinates
Hex triplet #0000FF
RGB (r, g, b) (0, 0, 255)
CMYK (c, m, y, k) N (100, 100, 0, 0)
HSV (h, s, v) (240°, 100%, 100%)
  N: Normalised to [ 0–255 ] (changing to [0–100])
For other uses, see Blue (disambiguation)

Blue is one of the three primary additive colors; blue light has the shortest wavelength range (about 420-490 nanometers) of the three additive primary colors. The English language commonly uses "blue" to refer to any color from blue to cyan.

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. For this reason, blue 80A filters are used to correct for the excessive redness of tungsten lighting in color photography.

Many languages do not have separate terms for blue and green, and in the Swedish language, blå, the modern word for blue, was used to describe black until the early 20th century. The modern English word blue comes from the Middle English, where it began to be used along with bleu, an Old French word of Germanic origin (possibly Old High German blao, "shining"). A Scots and Scottish English word for "blue" is blae, from the Middle English bla ("dark blue", from the Old English blæd).



A clear sky on a sunny day appears blue because of Rayleigh scattering of the light from the Sun. Large amounts of water appear blue because red light around 750 nm is absorbed as an overtone of the O-H stretching vibration. Interestingly, heavy water is colorless, because the absorption band (~950 nm) is outside the visible spectrum.

Plants and animals

A blue dog has a coat color that is primarily "bluish" gray or silver. Examples include the Kerry Blue Terrier with a solid "blue" coat and some Australian Shepherds and Border Collies, which have merle coats. (See also Blue Dog Democrats, below).

Symbolism and expressions

Picasso's Self-portrait with Cloak (1901)
Picasso's Self-portrait with Cloak (1901)

Blue often denotes injury, such as in the phrase "black and blue," since it is the color of a bruise. Blue is used also as a word to denote a sad or melancholy state, as in depression, or simply a state of deep contemplation (however, the phrase "blue skies," referring to sunny weather, implies cheerfulness). Symbolically, blue is associated with that state, such as the term blue period to describe Pablo Picasso's work form 1901 to 1904.

  • In Australia, a "blue" can also describe a fight or an argument. Men with red hair may be nicknamed "Bluey". The phrase "true blue" also means "genuine" (example : "He's a true blue Aussie").

A "blue joke" or "blue comedy" is comedy which uses references to socially taboo subjects such as sexual or lavatorial double entendre.

  • Because blue is traditionally the color of heaven, parents once wrapped their baby boys in blue to protect them from demons. Pink was later chosen as the color to associate with girls.
  • Blue is the color of the snooker ball which has a 5-point value.

Books and written works

A "blue book" is an almanac or similar reference work. For example, the Oregon Blue Book is the official directory and fact repository of the state of Oregon, while the Harvard Bluebook dictates a style of legal citation. The Blue Book is a term for a policy document issued by the Federal Communications Commission in the United States in 1946, urging television networks to uphold their commitment to public service. The Kelley Blue Book is a popular guide used for automobile prices.

Blue pages are a telephone directory of government offices—either an official blue book or a section of a commercial directory. Compare with the yellow pages or white pages.

In The Hitchhiker's Guide to the Galaxy there are several references to the Hooloovoo, "a super-intelligent shade of the color blue."


"Blue ribbon" is a term used to describe something of high quality, such as a blue-ribbon panel or a blue-ribbon commission. This comes from the practice of awarding blue ribbons for first place in competitions. The Blue Riband is a prize awarded since the 1860s to the ship that made the fastest trans-Atlantic crossing.

Math, science, and technology

"Big Blue" is a nickname for IBM. The company's chess computer (which defeated chess champion Garry Kasparov) was called Deep Blue. Users of Microsoft Windows often use the term "blue" to describe a computer that has encountered a "blue screen of death."

A blue box is an electronic device with a tone pulsator that simulates a telephone operator's dialing console by replicating the tones used to switch long-distance calls and using them to route the user's own call, bypassing the normal switching mechanism. They were used to avoid charges for telephone calls.

A "blue chip" is the nickname for a stock that is thought to be safe and in excellent financial shape. In the United States, $1 bills are delivered by the Federal Reserve Bank in blue straps.

In medical diagrams, blue is used to represent veins carrying deoxygenated blood back to the heart. Deoxygenated blood is actually reddish violet. When a medical patient is not getting enough oxygen or has stopped breathing, however, their skin often takes a blue tint, a condition called cyanosis.

In astronomy, 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 the expression "once in a blue moon" means "once in a great while" or "infrequently."

National, athletic, and university associations

This Israeli flag depicts a blue Star of David on a white background between two blue stripes. The color blue is mandated only as "sky blue," and the shade varies from flag to flag; sometimes it is a dark, almost navy blue, other times it is a very light blue.
This Israeli flag depicts a blue Star of David on a white background between two blue stripes. The color blue is mandated only as "sky blue," and the shade varies from flag to flag; sometimes it is a dark, almost navy blue, other times it is a very light blue.

Azzurro, a light blue, is the national color of Italy. Blue (along with white) is the national color of Israel and the color is seen on the Israeli flag.

Dark blue is associated with the University of Oxford and light blue with the University of Cambridge. The sporting colors of these universities are called "the blues."

A specific shade of dark blue is associated with Yale University. Blue Devils are the mascot of many American universities; Duke University's blue devils are the most famous but other universities with the mascot include Central Connecticut State University, Dillard University, Lawrence Technological University, State University of New York at Fredonia, and the University of Wisconsin-Stout.

The Columbus Blue Jackets are a National Hockey League team based in Columbus, Ohio. The Blue Jays are the mascots of the Toronto Blue Jays, a Major League Baseball team, and its two minor league affilates: the Dunedin Blue Jays in Dunedin, Florida, and the Pulaski Blue Jays in Pulaski, Virginia.

Social class and occupation

Blue may denote the working class, derived from the traditional color of factory uniforms. Blue-collar workers are industrial workers and are often contrasted white-collar office workers. However, in contrast to "blue collar," the phrase "blue blood" is used to mean "from an aristocratic background," because pale, untanned skin–a sign of notablity–allows blue-tinged veins to show through.

Several vocations are associated with blue. Law enforcement, and uniformed police, often wear blue uniforms and have become associated with the color, as seen in phrases such as "boys in blue," "blue line," and "blue wall." Most police cars have blue colors, and United Nations peacekeepers are uniformed in blue and white. "Bluecoat" (akin to "redcoat") refers to a uniformed police officer. Police in the People's Republic of China changed the color of their uniforms from green to blue in the late 1990s, partly to emphasize their civilian role. Since laws prohibit police from declaring a strike, the "blue flu" is a "sickout": a type of strike action in which police call in sick.

Blue is associated with many air forces and navies because of the color of their dress uniforms, while green is associated with armies. Navy blue is a particular shade of blue worn by sailors in the Royal Navy since 1748 and subsequently adopted by other navies around the world. The Blue Angels are an acrobatic flight squadron of the U.S. Navy.


Logo of the congressional Blue Dog Democrats.
Logo of the congressional Blue Dog Democrats.

Blue, like white, may represent authority as opposed to revolutionary red or black.

During the American Civil War, blue was used to represent the Union while gray represented the Confederacy. This representation was based on the uniforms worn by the respective armies, although uniforms remained non-standard thoughout the war and sometimes the colors were switched.

Internationally, blue is the symbol for conservatism and conservative political parties. There are several notable exceptions and different meanings.:


Blue is the color and name of the main character in the preschool animated television show Blue's Clues.

On Star Trek, medical and scientific personnel wear blue uniforms.


Blues is a music genre. A blue note is a note between the regular notes on the scale. Blue notes are the most important notes in the blues scale.

Bands called "Blue" include two British musical groups: the rock group Blue and the boy band Blue. Blue is the title of an album by the Canadian singer-songwriter Joni Mitchell, and Kind of Blue is the title of an album by Miles Davis, one of the world's best-selling jazz recordings.

Blue Train is an influential jazz album by John Coltrane. Rhapsody in Blue is a symphonic jazz composition for jazz band, piano, and orchestra by George Gershwin, while Love is Blue is a popular tune from the 1960s by Andy Williams, most notably performed by Paul Mauriat.

"Blue" has been used as a song title by many artists, notably LeAnn Rimes and Eiffel 65. Cristian Castro's song "Azul" (Spanish for "blue") repeats the line "This love is blue as the sea" (Este amor es azul como el mar).

Other songs which use the word blue include:

Use in painting

Traditionally, blue has been considered a primary color in painting, with the secondary color orange as its complement, but this is not consistent with modern scientific color theory. As the mixing of pigments is a subtractive color process, the true primary colors in painting and printing are cyan, magenta and yellow (with black often added for practical reasons; see CMYK color model).


Blue pigments


See also

External links

Look up blue on Wiktionary, the free dictionary.

Electromagnetic Spectrum

Gamma ray | X-ray | Ultraviolet | Optical spectrum | Infrared | Terahertz radiation | Microwave | Radio waves

Optical (visible) spectrum: Violet | Indigo | Blue | Cyan | Green | Yellow | Orange | Red

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