Cerulean may be applied to a range of colors from deep blue, sky-blue, bright blue or azure color through greenish blue colors.
The first recorded use of cerulean as a color name in English was in 1590. The word is probably derived from the Latin word caeruleus, "dark blue, blue or blue-green", which in turn probably derives from caelulum, diminutive of caelum, "heaven, sky".
In classical times, cerulean was used to describe blue pigments, particularly mixtures of copper and cobaltousoxides. These early attempts to create sky blue colors were often less than satisfactory due to greenish hues and lack of permanence. When the pigment 'cerulean blue' was invented, it largely superseded all these prior pigments.
Cerulean blue pigment
Discovered in 1805 by Andreas Höpfner, the pigment originally referred to as cerulean blue (or corruleum blue) was first marketed in 1860 as "coeruleum" by George Rowney of the United Kingdom. The primary chemical constituent of the pigment is cobalt(II) stannate.
It is particularly valuable for artistic painting of skies because of the purity of the blue (specifically the lack of greenish hues), its permanence (no other blue pigments retained color as well), and its opaqueness.
Today, cobalt chromate is sometimes marketed under the cerulean blue name but is darker and greener (Rex Art color index PB 36) than the cobalt stannate version (color index PB 35). The chromate makes excellent turquoise colors and is identified by Rex Art and some other manufacturers as "cobalt turquoise".
Cerulean in culture
The United States Navy Blue Angels aerobatics team wears, appropriately, uniforms that are a bright shade of cerulean. 
Cerulean Studios is a software house based in Connecticut, United States, notable for developing Trillian, an instant messaging client.
A pivotal scene in The Devil Wears Prada (film) explains how the character Andrea came to wear a cerulean blue sweater.
Cerulean is "the color of the sky on a serene, crystal clear day,"according to Pantone, Inc.
Cerulean is the name of a Boston-based IDM band.
Cerulean is the album title for the September 10, 1991 music release by the band The Ocean Blue
Cerulean Sky is the name of an Indianapolis-based band.
Cerulean is important in The X-Files episodes Pusher and Kitsunegari as a hypnotic catalyst a criminal uses (repeating cerulean over and over again to lull his victim).
There is a city and a gym badge named Cerulean in the Pokémon Kanto region, where Misty's family lives.
Cerulean is also the name of a city in the English translation of Pokémon Red and Blue.
Cerulean is a name given to Azul the Cerulean in Dirge of Cerberus -Final Fantasy VII- for his blue hair.
Cerulean is the described eye color of Squall Leonhart, the male protagonist in Final Fantasy VIII.
Cerulean is a planet in the N64 game Jet Force Gemini. The level consists of blue-green sand dunes.