Light-sensitive, purple-red organic pigment contained in the rod cells of the retina that allows the eye to see in black and white in dim light. It is composed of opsin, a protein, linked to retinal, a conjugated molecule (see conjugation) formed from vitamin A. Photons of light that enter the eye are absorbed by retinal and cause it to change its configuration, starting a biochemical chain of events that ends with impulses being sent along the optic nerve to the brain. In bright light, to protect rod cells from overstimulation, rhodopsin breaks down into retinal and opsin, both of which are colourless. In dim light or darkness the process is reversed (dark adaptation), and purple-red rhodopsin is reformed. Similar light-sensitive compounds made of retinal and other opsin proteins are the pigments in the retina's cone cells responsible for colour vision in bright light.
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Purple is a general term for the range of shades of color occurring between red and blue. It is formed (in both subtractive pigment and additive light combinations) by mixing the primary colors red and blue in varying proportions, with possibly a very small quantity of the third primary color (green for light or yellow for pigment). There is disagreement over exactly which shades can be described as purple, some people preferring more precise terms such as magenta or heliotrope for particular shades. A difference in retinal sensitivity to red and blue light between individuals can cause further disagreement.
In human color psychology, purple is associated with royalty, regality, and nobility (stemming from its use in heraldry to denote gentry).
The word 'purple' comes from the Old English word purpul which originates from the Latin purpura. This in turn is derived from the Koine Greek πορφύρα (porphyra), name of the dye manufactured in Classical antiquity from the mucus-secretion of the hypobranchial gland of a marine snail known as the Murex brandaris or the spiny dye-murex.
The first recorded use of the word 'purple' in English was in the year AD 975.
Violet is a spectral color (approximately 420–380nm), of a shorter wavelength than blue, while purple is a combination of red and blue or violet light. The purples are colors that are not spectral colors – purples are extra-spectral colors. In fact, purple was not present on Newton's color wheel (which went directly from violet to red), though it is present on modern ones, between red and violet. There is no such thing as the "wavelength of purple light"; it only exists as a combination.
On the CIE xy chromaticity diagram, violet is on the curved edge in the lower left, while purples are the straight line connecting the extreme colors red and violet.
One interesting psychophysical feature of the two colors that can be used to separate them is their appearance with increase of light intensity. Violet, as light intensity increases, appears to take on a far more blue hue as a result of what is known as the Bezold-Brücke shift. The same increase in blueness is not noted in purples.
Violet cannot be reproduced by a Red-Green-Blue (RGB) color system, and must be simulated by a mixture of red and blue (purple). The shade of violet simulated in the color box above is just over halfway between magenta and blue on the color wheel.
On a chromaticity diagram, the straight line connecting the extreme spectral colors (red and violet) is known as the 'line of purples' (or 'purple boundary'); it represents one limit of human color perception. The color magenta used in the CMYK printing process is on the line of purples, but most people associate the term "purple" with a somewhat bluer shade. Some common confusion exists concerning the color names "purple" and "violet". Purple is a mixture of red and blue light, whereas violet is a spectral color.
The actual color of Tyrian purple, the original color purple from which the name purple is derived, is the color of a dye made from a mollusk that, because of its incredible expense (many times more expensive than gold), in classical antiquity became a symbol of royalty because only the very wealthy could afford it. Therefore, Tyrian purple is also called imperial purple.
Tyrian purple may have been discovered as early as the time of the Minoan civilization. Alexander the Great (when giving imperial audiences as the emperor of the Macedonian Empire), the emperors of the Seleucid Empire, and the kings of Ptolemaic Egypt wore Tyrian purple. The imperial robes of Roman emperors were Tyrian purple trimmed in metallic gold thread. The badge of office of a Roman Senator was a stripe of Tyrian purple on their white toga. Tyrian purple was continued in use by the emperors of the Eastern Roman Empire until its final collapse in 1453.
Han purple is a purple in the sense that the term is used in colloquial English, i.e., it is a color between red and blue; however, it is not a purple in the sense that the term is used in color theory, i.e. a non-spectral color between red and violet on the line of purples on the CIE chromaticity diagram.
This shade of purple is bluer than the ancient Tyrian purple.
In medieval Europe, blue dyes were rare and expensive, so only the most wealthy or the aristocracy could afford to wear them. (The working class wore mainly green and brown.) Because of this (and also because Tyrian purple had gone out of use in western Europe after the collapse of the Western Roman Empire in AD 476), Europeans' idea of purple shifted towards this more bluish purple known as royal purple because of its similarity to the royal blue worn by the aristocracy. This was the shade of purple worn by kings in medieval Europe.
'Royal purple' (shown above) or the dark violet color known as vulgar purple is the common layman's idea of purple, but professional artists, following Munsell color system (introduced in 1905 and widely accepted by 1930), regard purple as being synonymous with the red-violet color shown at right, in order to clearly distinguish purple from violet and thus have access to a larger palette of colors. This red-violet color, called artist's purple by artists, is the pigment color that would be on a pigment color color wheel between pigment violet and pigment (process) magenta. In the Munsell color system, this color at the maximum chroma of 12 is called Red-Purple.
Artists pigments and colored pencils labeled as purple are colored the red-violet color shown at right.
Using additive colors such as those on computer screens, it is possible to create a much brighter purple than with pigments where the mixing subtracts frequencies from the component primary colors. The equivalent color on a computer to the pigment color red-violet shown above would be this electric purple, i.e. the much brighter purple you can see reproduced on the screen of an electronic computer. This color is pure purple conceived as computer artists conceive it, as the pure chroma on the computer screen color wheel halfway between electric violet and electric magenta. Thus, electric purple is the purest and brightest purple that it is possible to display on a computer screen.
This color may be called HTML/CSS purple.
See the chart Color names that clash between X11 and HTML/CSS in the X11 color names article to see those colors which are different in HTML and X11.
This color can be called X11 purple.
Displayed at right is the web color medium purple.
This color is a medium shade of the bright X11 purple shown above.
The color orchid is a light shade of purple. The name 'orchid' originates from the flowers of some species of the vast orchid flower family, such as Laelia furfuracea and Ascocentrum pusillum, which have petals of this color.
The color heliotrope is a brilliant shade of purple.
In the 1980s there was a Jimi Hendrix Museum in a Victorian house on the east side of Central Ave. one half block south of Haight Street in the Haight-Ashbury neighborhood of San Francisco which was painted this color.
The first recorded use of Mulberry as a color name in English was in 1776.
The pansy flower has varieties that exhibit three different colors: pansy (a deep shade of violet), pansy pink, and pansy purple.
The first recorded use of Pansy Purple as a color name in English was in 1814.
Roses are red, violets are purple Sugar is sweet and so is maple surple [sic]gay community.