Azure (color)

Azure is a bright, cyan-blue color named after the rock lapis lazuli. It is often described as the color of the sky on a clear day.
On the :File:RBG color wheel.svg|RGB color wheel, "azure" is defined as the color at 210 degrees, i.e., the hue halfway between blue and cyan. In the RGB color model, used to create all the colors on a television or computer screen, azure is created by adding a little green light to blue light. The complementary color of azure is orange.
In the X11 color system, which became a standard for early web colors, azure is depicted as a pale cyan or white cyan.

Etymology and history

The color azure ultimately takes its name from the intense blue mineral lapis lazuli. Lapis is the Latin word for "stone" and lāzulī is the genitive form of the Medieval Latin lāzulum, which is taken from the Arabic لازورد lāzaward, itself from the Persian لاژورد lāžaward, which is the name of the stone in Persian and also of a place where lapis lazuli was mined.
The name of the stone came to be associated with its color. The French azur, the Italian azzurro, the Polish lazur, Romanian azur and azuriu, the Portuguese and Spanish azul, Hungarian azúr, and the Catalan atzur, all come from the name and color of lapis lazuli.
The word was adopted into English from the French, and the first recorded use of it as a color name in English was in 1374 in Geoffrey Chaucer's work Troilus and Criseyde, where he refers to "a broche, gold and asure".
Azure also describes the color of the mineral azurite, both in its natural form and as a pigment in various paint formulations. In order to preserve its deep color, azurite was ground coarsely. Fine-ground azurite produces a lighter, washed-out color. Traditionally, the pigment was considered unstable in oil paints, and was sometimes isolated from other colors and not mixed.
The use of the term spread through the practice of heraldry, where "azure" represents a blue color in the system of tinctures. In engravings, it is represented as a region of parallel horizontal lines, or by the abbreviation az. or b. In practice, azure has been represented by any number of shades of blue. In later heraldic practice a lighter blue, called bleu celeste, is sometimes specified.

Distinction among indigo, azure and cyan

According to the logic of the :File:RBG color wheel.svg|RGB color wheel, indigo colors are those colors with hue codes between 255 and 225, azure colors are those colors with hue codes between 195 and 225, and cyan colors are those colors with hue codes between 165 and 195. Another way of describing it could be that cyan is a mixture of blue and green light, azure is a mixture of blue and cyan light, and indigo is a mixture of blue and violet light.
All of the colors shown below in the section shades of azure are referenced as having a hue between 195 and 225 degrees, with the exception of the very pale X11 web color azure - RGB - which, with a hue of 180 degrees, is a tone of cyan, but follows the artistic meaning of azure as sky blue.

Azure in nature

The true color of the exoplanet HD 189733b determined by astronomers is azure blue.