The first recorded use of sky blue as a color name in English was in 1728 in the Cyclopædia of Ephraim Chambers. Prior to the Chambers reference, the color had first been used in 1585 in a book by Nicolas de Nicolay where he stated "the tulbant of the merchant must be skie coloured".
Deep sky blue is an azure-cyan color associated with deep sky blue.
This color is on the color wheel (RGB/HSV color wheel) halfway between azure and cyan.
The traditional name for this color is Capri.
The first use of Capri as a color name in English was in 1920.
The color Capri in general is named for the azure-cyan color of the Mediterranean Sea around the island of Capri off Italy, the site of several villas belonging to the Roman Emperor Tiberius, including his imperial residence in his later years, the Villa Jovis. Specifically, the color Capri is named after the color of the Blue Grotto on the island of Capri as it appears on a bright sunny day. Today the island of Capri is a resort island popular with tourists.
The name deep sky blue for this color did not come into use until the promulgation of the X11 color list in 1987.
The color true blue is a deep tone of azure that is the color of the uniforms of the sports teams of UCLA. It is also one of the shades of blue used by the Los Angeles Chargers though they use the name powder blue.
The color air force blue, also known as RAF blue. This is the tone of air force blue used by the Royal Air Force, the first air force to choose an "air force blue" color by which to identify itself, in 1920.
The color "air force blue" is a medium tone of azure since it has a hue code of 204 which is a hue code between 195 and 225, signifying a tone of azure.
The color defined as blue in the NCS or Natural Color System is an azure-like color shown at right (NCS 2060-B). The Natural Color System is a color system based on the four unique hues or psychological primary colors red, yellow, green, and blue. The NCS is based on the opponent process theory of vision.
The “Natural Color System” is widely used in Scandinavia.
The color defined as blue in the Munsell color system (Munsell 5B) is shown at right. The Munsell color system is a color space that specifies colors based on three color dimensions: hue, value (lightness), and chroma (color purity), spaced uniformly (according to the logarithmic scale which governs human perception) in three dimensions in the Munsell color solid, which is shaped like an elongated oval at an angle. In order for all the colors to be spaced uniformly, it was found necessary to use a color wheel with five primary colors: red, yellow, green, blue, and purple.
Munsell can only be displayed approximately on a computer screen, as these spectral colors have been adjusted to fit into the sRGB gamut. In the 21st century, this hue is classified as an intermediate between azure and cyan.
Uranian blue is a light greenish blue, the color of Uranus.
In this section, the term shade is used in its technical sense as used in color theory, meaning a blueish color mixed with black or dark gray. The colors arranged in order of their value (brightness) (V in the HSV code), the brighter colors toward the top and the darker colors toward the bottom.
Spanish blue is the color that is called Azul (the Spanish word for "blue") in the Guía de coloraciones (Guide to colorations) by Rosa Gallego and Juan Carlos Sanz, a color dictionary published in 2005 that is widely popular in the Hispanophone realm. It is a shade of azure.
Berkeley Blue is one of the official colors of the University of California, Berkeley, along with California Gold. Until 2007, the university had used Yale Blue in its place, given Berkeley's historical ties to Yale University, particularly in its founding. Berkeley's school colors are the originators for those of all the campuses in the University of California system, of which Berkeley is the oldest as its flagship.
Celtic blue is a shade of blue, also known as glas celtig in Welsh, or gorm ceilteach in both the Irish language and in Scottish Gaelic. Julius Caesar reported (in Commentarii de Bello Gallico) that the Britanni used to colour their bodies blue with vitrum, a word that means primarily "glass", but also the domestic name for the "woad" (Isatis tinctoria), besides the Gaulish loanword glastum (from Proto-Celtic *glastos "green"). The connection seems to be that both glass and the woad are "water-like" (lat. vitrum is from Proto-Indo-European *wed-ro- "water-like").
Yale Blue is the dark azure color used in association with Yale University. The hue of Yale Blue is one of the two official colors of Indiana State University, the University of Mississippi, and Southern Methodist University. The official color "DCU Blue" of Dublin City University is very close to Yale Blue.
Yale Blue was also an official color of University of California, Berkeley, and Duke University.
Penn Blue is one of the official colors of the University of Pennsylvania, along with Penn Red. While the school colors were defined by 1910, university history points to earlier times when the colors may have been chosen, including a possible visit by George Washington to the University, where students used the color of his tunic to determine school colors or a track meet where Penn athletes declared that they would wear the colors "of the teams we beat," which would be those of both Harvard University and Yale University. Originally defined as the colors used on the American flag, the colors have since deviated.