red green blue
Color is a function of the human visual system, and is not an intrinsic property. Objects don"t have a color, they give off light that appears to be a color. Spectral power distributions exist in the physical world, but color exists only in the mind of the beholder. Our perception of color is not an objective measure of anything about the light that enters our eyes, but it correlates pretty well with objective reality.
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Color is determined first by frequency and then by how those frequencies are combined or mixed when they reach they eye. This is the lifwynnfoundation.org part of the topic. Light falls on specialized receptor cells (called cones) at the back of the eye (called the retina) and a signal is sent to the brain along a neural pathway (called the optic nerve). This signal is processed by the part of the brain near the back of the skull (called the occipital lobe). Here"s where the biology kicks in, or maybe it"s the psychology, or maybe it"s both. They eye is very much like a camera, but the brain is not at all like a video recorder. The brain is not like a computer with fixed hardware of transistors and capacitors executing some sort of software code. The neurons of the brain are probably best thought of as wetware — a fusion of hardware and software or maybe something completely different. I don"t feel qualified to say much about that end of this process. Once the visual information leaves the eye, basic lifwynnfoundation.org ends and neurocognition takes over.
Color is determined first by frequency. Let"s start by determining what a typical person would see when looking at electromagnetic radiation of a single frequency. Physicists call this monochromatic light. (The literal meaning of this word is "single color", but the actual meaning is "single frequency".)
Low frequency radiation is invisible. With an adequately bright source, starting somewhere around 400 THz (1THz=1012Hz) most humans begin to perceive a dull red. As the frequency is increased, the perceived color gradually changes from red to orange to yellow to green to blue to violet. The eye doesn"t perceive violet so well. It always seems to look dark compared to other sources at equal intensity. Somewhere between 700THz and 800THz the world goes dark again.
How many colors are there in the spectrum above? How many did I name?
The simple named colors are mostly monosyllabic English words — red, green, brown, black, white, gray. Brevity indicates an Old English (Anglo-Saxon) origin. Monosyllabic words are generally the oldest words in the English language — head, eye, nose, foot, cat, dog, cow, eat, drink, man, wife, house, sleep, rain, snow, sword, sheath, God…. These words go back more than fifteen centuries. Yellow, purple, and blue are exceptions to the one-syllable-equals-English rule. Yellow and purple are Old English color words with two syllables. Blue is a one syllable French word (bleu) that replaced a two syllable Old English word (hǽwen) eight hundred years ago.
Some of the names for colors are loan words from French (many of which are loan words from other languages). Since the ʒ (zh) sound doesn"t exist in Old English, orange and beige are obviously French. (Garage is also an obviously French word.) The words violet and orange were the names of plants (nouns) before they were the names of colors (adjectives). Violet came from 14th century French, which came from Latin. Orange came from 16th century French, which came from Italian, which came from Arabic, which came from Persian, which came from Sanskrit.
English arose when three Germanic tribes — Angles, Saxons, and Jutes — migrated from continental Europe to the British Isles in the 5th century. The language they spoke is called Anglo-Saxon or Old English. You would hardly recognize this language if you heard it spoken or saw it written today. Danes probably have the best chance of understanding spoken Old English, Icelanders the best chance of understanding written Old English. Of the six named colors in my spectrum, only four were known to the Anglo-Saxons: reád, geolu, grÉne, hǽwen. Do you recognize any of them?
In the year 1066, an invasion of French speaking peoples — Normans, Bretons, and French — swept over the British Isles. The last Anglo-Saxon King of England, King Harold II, was succeeded by the first Norman king, William the Conqueror. The Normans had an odd empire (if that"s even the word for it) that included the British Isles, northern France (appropriately named Normandy), southern Italy, Sicily, Syria, Cyprus, and Libya. William was a Norman, descended from Norsemen, but he spoke French not Swedish or Norwegian or Danish. One factor leading to the rise of the Normans in their scattered empire is their ability to quickly integrate themselves into the culture of the peoples they conquered. For purposes of this discussion, we care about language. When the Normans got to northern France, they started speaking French. When the Normans got to England they got the Anglo-Saxons to start speaking French too (sort of). In about a hundred years, Anglo-Saxon had mutated into something closer to what we would recognize as English today — neither French nor Anglo-Saxon. Old English became Middle English. This is when English acquired the words blue (which replaced hǽwen) and violet (which never existed as an English color word before).
The next change in the English language was one of pronunciation — the Great Vowel Shift (1400–1700). This is when silent e and other spelling rules that frustrate both native and second language speakers arose. The notion of long and short vowels also changed. At one time a long vowel was one that was pronounced for a longer time than a short vowel. Take the words pan and pane. Before the Great Vowel Shift, pan was pronounced "pan" and pane was pronounced "paaaneh" with a literal looong vowel and a non-silent "eh" at the end. Being mostly a change in pronunciation, the rise of Modern English around 1550 doesn"t affect our discussion of color words. Movable type printing invented in Germany around 1445 is probably more important. Books became relatively plentiful, spelling became standardized, and tracking down the first occurrence of a word became easier. The Modern English period is when the words orange and indigo were first used to identify colors.
I have issues with indigo. More on that later.
|red(reád)||on ðæs sacerdes hrægle scoldon hangigan bellan & ongemang ðæm bellum reade apla.on the priest"s robe should hang bells and among the bells, red apples.King Alfred"s West-Saxon version of Pope Gregory"s Pastoral Care (~870)|
|yellow(geolu)||Uyrmas mec ni auefun uyrdi cræftum, ða ði geolu godueb geatum frætuath.Worms did not weave me with the skills of the fates, those that decorated the yellow cloth garment.The Leiden Riddle (~900)|
|green(grÉne)||siððan adam stop on grene græs, gaste geweorðad.since Adam stepped on green grass, possessed of life.The Genesis A, B story from the Cædmon Manuscript (~950)|
|blue(hǽwen)||þou schalt þeos þreo cloþes do a non ech of heom in o Caudroun, for ich þe wolle segge sothþ þat þis on schal beo fair blu cloth, þis oþur grene, onder stond þis!Altenglische legenden a.k.a. Old English Legends compiled by Carl Horstmann (~1300)|
|violet(n/a)||In Inde also may men fynd dyamaundz of violet colour and sum what browne, þe whilk er riȝt gude and full precious.In India also men may find diamonds of violet colour (and somewhat brown), which are right good and full precious.The Buke of John Maundeuill a.k.a. Mandeville"s Travels (1425)|
|orange(n/a)||no Person or Persons shall put to sale by Retail within this Realm any Cloth or Clothes … of other Colour or Colours than is hereafter expressed; that is to say, Scarlet, Red, Crimson, Murry, Violet, Puke, Brown-blue, Blacks, Greens, Yellows, Blues, Orange-tauny, Russet, Marble-gray, Sad new Colour, Azure, Watchet, Sheeps-colour, Lion-colour, Motley or Iron grayGreat Britain Statutes at Large (1552)|
|indigo(n/a)||For a deepe and sad Greene, as in the inmost leaves of Trees, mingle Indico and Pinke.The Compleat Gentleman by Henry Peacham (1622)|
There is no physical significance in color names. It"s all a matter of culture and culture depends on where you live, what language you speak, and what century it is. A given wave of light has the same frequency no matter who is viewing it, but the person perceiving the color will call it a word appropriate to their culture.
Color discrimination is probably the same for all people in all cultures (all people with properly working eyeballs). Did the English see orange or violet before the French told them about it? Of course they did. They probably called orange reád (red) or geolo-reád (yellow-red) and violet hǽwen (blue) or blæc-hǽwen (dark blue) because those were the words they had available.
Why is an orange called an orange but a lemon not called a yellow and a lime not called a green?
What would you call indigo if I showed it to you? Most certainly blue. I don"t know anyone who uses the word indigo in everyday conversation. Maybe some painters do. That"d be about it for indigo as far as Modern English speakers were concerned. In some languages blue and indigo are equally significant color words. Maybe the real question is do we need blue, indigo, and violet?
Frequency determines color, but when it comes to light, wavelength is the easier thing to measure. A good approximate range of wavelengths for the visible spectrum is 400nm to 700nm (1nm=10−9m) although most humans can detect light just outside that range. Since wavelength is inversely proportional to frequency the color sequence gets reversed. 400nm is a dull violet (but violet always appears dull). 700nm is a dull red.
Wavelength varies with the speed of light, which varies with medium. The speed of light is about 0.03% slower in air than in vacuum. If you"re trying to understand color, wavelength is just as good as frequency.
We humans who speak English and live at the dawn of the 21st century have identified six wavelength bands in the electromagnetic spectrum as significant enough to warrant a designation with a special name. They are: red, orange, yellow, green, blue, and violet. Where one color ends and another begins is a matter of debate as you will see in the table below.
Which brings us to indigo. How many of you reading this learned about "RoyG.Biv" (Americans, I presume) or that "Richard of York gave battle in vain" (Britons, I presume)? Who among you learned that between blue and violet there was this special color called indigo?
Indigo. The only time I ever hear it is when my students recite the visible spectrum. Indigo is a color of relatively little importance. If indigo counts as a color then so should canary, and mauve, and puce, and brick, and teal, and so on. Where is their place in the spectrum?
How many colors are there in this swatch? How many were you taught in elementary school? The inclusion of indigo in the spectrum goes back to Isaac Newton. More on this after the data table. If you believe that indigo is an important color, then here"s a set of spectral tables for you.
Did Richard of York give battle in vain so that future citizens in the dismantled British Empire would forever remember indigo? Did Mr. and Mrs. Biv conceive little Roy G. so that future generations of Americans might learn the true nature of light? Where did indigo come from?
When Newton attempted to reckon up the rays of light decomposed by the prism and ventured to assign the famous number seven, he was apparently influenced by some lurking disposition towards mysticism, If any unprejudiced person will fairly repeat the experiment, he must soon be convinced that the various coloured spaces which paint the spectrum slide into each other by indefinite shadings: he may name four or five principal colors, but the subordinate spaces are evidently so multiplied as to be incapable of enumeration. The same illustrious mathematician, we can hardly doubt, was betrayed by a passion for analogy, when he imagined that the primary colours are distributed over the spectrum after the proportion of the diatonic scale of music, since those intermediate spaces have really no precise defined limits.
John Leslie, 1838
basic colour names, pl eleven colour names found in anthropological surveys to be in wide use in fully developed languages: white, black, red, green, yellow, blue, brown, grey, orange, purple, pink
The human eye can distinguish something on the order of 7 to 10 million colors — that"s a number greater than the number of words in the English language (the largest language on Earth).
The rods, which far outnumber the cones, respond to wavelengths in the middle portion of the spectrum of light. If you had only rods in your retina, you would see in black and white. The cones in our eyes provide us with our color vision. There are three types of cone, identified by a capital letter, each of which responds primarily to a region of the visible spectrum: L to long or red, M to medium or green, and S to shirt or blue.
The peak sensitivities are 580nm for red (L), 540nm for green (M), and 440nm for blue (S). Red and green cones respond to nearly all visible wavelengths, while blue cones are insensitive to wavelengths longer than 550nm. The total response of all three cones together peaks at 560nm — somewhere between yellow and green in the spectrum.
Paraphrase…While red, green, and blue are spaced somewhat equally across the visible spectrum, the specific sensitivities of the L, M, and S cones are not. This might seem a little confusing, especially since the L cones aren"t even closely centered on the red area of the spectrum. Fortunately, the spectral sensitivity of the cones is only one part of how the brain decodes color information. Additional processing takes these sensitivities into account.
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Commission internationale de l"eclairage
The relative response of the red and green cones to different colors of light are plotted on the horizontal and vertical axes, respectively. Values on the tongue shaped perimeter are for light of a single wavelength (in nanometers). Values within the curve are for light of mixed frequency. The point in the center labeled D65 corresponds to light from a blackbody radiator at 6500K — the effective temperature of daylight at midday, a generally accepted standard value of white light.
white & black
Continuous, thermal spectra
|blackbody color by temperature|
|2.73||cosmic background radiation|
|500||household oven at its hottest|
|660||minimum temperature for incandescence|
|770||dull red heat|
|1,400||glowing coals, electric stove, electric toaster|
|2,800||incandescent light bulb, 75W|
|2,900||incandescent light bulb, 100W|
|3,000||incandescent light bulb, 200W|
|3,100||sunrise or sunset (effective)|
|3,200||professional studio lights|
|3,600||one hour after sunrise or one hour before sunset (effective)|
|4,000||two hours after sunrise or two hours before sunset (effective)|
|5,500||direct midday sunlight|
|7,000||overcast sky (effective)|