Yellow is the color evoked by light that stimulates both the L and M (long and medium wavelength) cone cells of the retina about equally, with no significant stimulation of the S (short-wavelength) cone cells. Light with a wavelength of 570–580 nm is yellow, as is light with a suitable mixture of somewhat longer and shorter wavelengths. Yellow's traditional RYB complementary color is purple, violet, or indigo, while its colorimetrically defined complementary color in both RGB and CMYK color spaces is blue.

Etymology and definitions

thumb|Jaundice in a man with hepatic failure The word yellow comes from the Old English geolu, or geolwe which derived from the Proto-Germanic word gelwaz. The oldest known use of this word in English is in the Old English poem Beowulf, in a description of a shield made of wood from a yew tree.Oxford English Dictionary

In the English language, yellow has traditionally been associated with jaundice and cowardice. Yellow is associated with the word "caution" and is the second light on stop lights; in American slang, a coward can be said to be "yellowbellied" or "yellow". The color is associated with aging as well, for both people and objects (e.g. "yellowed" paper). Ethnographically, the term "yellow" has been used as a slang term for both Oriental persons ("yellow peril") and, in the early 20th century, light-skinned African-Americans (High yellow).

"Yellow" ("giallo"), in Italy, refers to crime stories, both fictional and real. This association began in about 1930, when the first series of crime novels published in Italy had yellow covers. The term "yellow movie" (黃色電影) can refer to films of pornographic nature in Chinese culture, and is analogous to the English "blue movie". Lastly, it is associated with sensational journalistic practices, or yellow journalism, and resistance to militant trade unions.

Colorimetry

Astronomy

Stars of spectral classes F and G, such as our sun Sol, have color temperatures that make them look "yellowish". The first astronomer to classify stars according to their color was F. G. W. Struve in 1827. One of his classifications was flavae, or yellow, and this roughly corresponded to stars in the modern spectral range F5 to K0. The Strömgren photometric system for stellar classification includes a 'y' or yellow filter that is centered at a wavelength of 550 nm and has a bandwidth of 20–30 nm.

Biology

• The yellow birch (Betula alleghaniensis) is a birch species native to eastern North America, from Nova Scotia, New Brunswick, and southern Quebec west to Minnesota, and south in the Appalachian Mountains to northern Georgia. They are medium-sized deciduous trees and can reaching about 20 m tall, trunks up to 80 cm in diameter. The bark is smooth and yellow-bronze and the wood is extensively used for flooring, cabinetry, and toothpicks.