Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal mixture of red and green light. On a colour wheel based on traditional colour theory (RYB) where blue was considered a primary colour, its complementary colour is considered to be orange (based on the Munsell colour wheel). The English language commonly uses "blue" to refer to any colour from navy blue to cyan. The word itself is derived from the Old French word bleu.
The modern English word blue comes from Middle English bleu or blewe, from Old French bleu, bleve, blöe, a word of Germanic origin (Frankish or possibly Old High German blāo, "blue"). Bleu replaced Old English blāw "blue" and blǣwen ...view middle of the document...
As a curiosity, blue is thought to be cognate with black, blond, and bleach, in the sense of blank, and through the Germanic word. Through a Proto-Indo-European root, it is also linked with Latin flavus ("yellow"; see flavescent and flavine), with Greek phalos (white), French blanc (white, blank) (borrowed from Old Frankish), and with Russian белый, belyi ("white," see beluga), and Welsh blawr (grey) all of which derive (according to the American Heritage Dictionary) from the Proto-Indo-European root *bhel- meaning "to shine, flash or burn", (more specifically the word bhle-was, which meant light coloured, blue, blond, or yellow), whence came the names of various bright colours, and that of colour black from a derivation meaning "burnt" (other words derived from the root *bhel- include bleach, bleak, blind, blink, blank, blush, blaze, flame, fulminate, flagrant and phlegm).
In the English language, blue may refer to the feeling of sadness. "He was feeling blue". This is because blue was related to rain, or storms, and in Greek mythology, the god Zeus would make rain when he was sad (crying), and a storm when he was angry. Kyanos was a name used in Ancient Greek to refer to dark blue tile (in English it means blue-green or cyan). The phrase "feeling blue" is linked also to a custom among many old deepwater sailing ships. If the ship lost the captain or any of the officers during its voyage, she would fly blue flags and have a blue band painted along her entire hull when returning to home port.
The adjective BLUE meaning "sad," a usage first recorded in Chaucer's Complaint of Mars (c. 1385).
The noun BLUES, meaning "low spirits," was first recorded in 1741.
The blues is a shortening of BLUE DEVILS, demons popularly thought to cause depression and sadness. Blue devils have been around since 1616.
Many languages do not have separate terms for blue and or green, instead using a cover term for both (when the issue is discussed in linguistics, this cover term is sometimes called grue in English).