Question: Which of these colors — red, orange, yellow, green, cyan, blue, magenta — never existed in the spectrum, let alone in a rainbow?

In physics the visible spectrum extends from red at the long-wave end to blue at the other. But artistically we think of it as a continuous circle or wheel with an extraspectral realm of hues centering on magenta — none of which exist as a wavelength — bridging those two ends.

Our brains work that magic on us whenever we see a color that has some red and some blue but little or nothing between.

That’s right. Magenta is imaginary.

For some hypothetical fun, picture that situation as a bell curve of light at the red end and an identical bell curve at the blue end, causing us to perceive magenta (1).

Now let’s start sliding those two bumps together toward the middle. You’ll see the saturation decrease (2) until it reaches neutral gray (3). As the bumps keep drawing closer to each other (4), you’ll notice the saturation picking back up again but now it’s greenish. As they merge into a single bell curve at the center of the visual spectrum (5), you see fully saturated green.

So there you are: Two light sources on either side of green will average out to green to you if they’re fairly close to each other. But if they’re far enough apart, they still average green in reality but instead you see magenta. Enjoy it. We’re wired that way.

Now those purplish hues can show up in partially or fully doubled rainbows where the blue of one overlaps the red of another. But neither by itself can display them because they simply don’t exist.

elow are some of the rarest or otherwise most intriguing colors you’ll likely encounter, including an option to change their ordering style, should you like, to make certain types easier to locate.

History, surprise, nostalgia, decorating ideas, and maybe even a few cheap thrills await as you ROLL OVER each of the swatches to see their stories.

While quite a few of these colors are solidly standardized, others in this set reflect some difference-splitting among conflicting sources or, at the very least, educated guessing.* Of the earthbound specimens, some are liquids (dyes), some are solids (pigments), and one is actually a gas.

Good, powerful blues that don’t fade or change color have always been tricky to pull off, so it can be illuminating to see how different eras and technologies rose to that challenge. When it comes to a purple dye, Mauve, there seems to be some dispute. We tend to think of that color as a rather soft-spoken one — subtle and grayish. But since the original swatch dating back to its 1856 discovery looks like anything but, that’s the version I show.

Hershey’s trademark purplish brown, which the company calls “Dark Sienna” and whose RGB of 56-18-22 must be etched in stone somewhere, is one of my more recent additions. If you should come across another color you think might fit into this assortment — a truly distinctive one with a rolicking good story — do let me know.

Again, just ROLL YOUR CURSOR over each swatch to find out about it.

Select sample order:

· Conversational Default   · Alphabetical   · By Hue   · By Brightness   · By Saturation

Traditional color of cottages and barns in Finland, Norway, and Sweden that came to represent idyllic farm life. The paint was a mixture of water, rye flour, linseed oil, and red mining sludge (silicates, iron oxides, copper compounds, and zinc) that you cooked. As it crumbled in time, you simply sloshed new paint over the old.

Falu

V Hydrae is a huge, pulsating red carbon star — in fact, the reddest star known. Most of its hydrogen has fused to helium, which in turn is now fusing into carbon, silicon, and oxygen. The silicon carbide, carbon monoxide and dioxide, and plain old carbon grit in its atmosphere block all but the star’s infra-red and red light.

V Hydrae

This almost preternatural-looking dye comes from the resin of certain types of plants, perhaps most aptly the Canary Island Dragon tree. Aside from its coloring value, it has seen use as a varnish for violins, an incense resin, a toothpaste, a folk cure for a variety of ills, and an indispensable ingredient for alchemists and practitioners of ritual magic.

Dragon’s Blood

This is cinnabar, mercury sulfide. To modern sensibilities insidiously toxic, though artists from antiquity until well into the 20th century could never have managed without it. For this pigment, particle size determined the precise hue.

Vermilion

To achieve this red, clothing was dyed by an insanely laborious process involving rose madder, sheep’s blood, sheep’s dung, gall nut, olive oil, potassium tartrate, alum, lye, and a dollop of lead acetate for good measure. Popular during the 18th, 19th centuries.

Turkey

Whenever an alchemist makes gold, the philosopher’s stone, or a medical cure-all, there will invariably be a rusty residue left behind. In Latin it’s caput mortuum or “dead head.” As a pigment it’s a deep reddish hematite (Fe2O3) and as “Cardinal Purple” to painters it lent a quiet dignity to the robes of popes, saints, and their better-heeled art patrons.

Caput Mortuüm

Since butter and Cheddar often come out white or nearly so, manufacturers rely on Annatto dye to correct that. Orange when concentrated and yellow when dilute, it’s been used as a colorant and subtle flavoring for centuries (“slightly nutty, sweet and peppery”). It comes from the seeds of the tropical achiote tree.

Annatto

Toxic arsenic disulfide, used widely by artists until the mid 18th century. Per ancient Chinese tradition, people drank an orange rice wine brewed with Realgar during the Dragon Boat Festival. As they say, it’s the dose that makes the poison as arsenic can also treat acute promyelocytic leukemia.

Realgar

Roast white lead pigment in the air and you get Minium. Highly popular for many centuries, especially among the medieval scribes who created illuminated manuscripts. Also highly toxic, though still used in paints in Russia, Norway, India, and China.

Minium

“I shall only say that the fuel they use for the locomotive is composed of [Egyptian] mummies three thousand years old,” wrote Mark Twain in Innocents Abroad. The reality was little different, as they were routinely ground up for use in medical concoctions and a cinnamon-colored artist’s pigment.

Mummy

Named for Sienna, Italy, a mined product of iron and manganese oxides. One of our most ancient pigments, a favorite of prehistoric cave painters. Turns into burnt sienna (lower right) when it’s strongly heated.

Sienna

Dark and very slightly brown with a 14% reflectance similar to that of Mercury. The Moon is receding from us at around an inch and a half per year. (Black shown lower left corner for comparison.)

Moon

We’ve known Pluto was orangish for many years. New Horizons clinched it in 2015. The Chinese name of this planet translates to “Star of the King of Hell.”

Pluto

Umber, raw and burnt. Named for its classical source, the mountainous region of Umbria, Italy. Like Sienna but of different proportions and impurities, it consists of iron and manganese oxides. When baked in a kiln it becomes burnt umber.

Umber

Likely much darker than you thought, as it looks orange against a black sky. Planet-wide dust storms sometimes kick up and convert Mars into a featureless rust-colored globe for weeks at a time and atmospheric pressure there can vary by a factor of almost 40.

Mars

Those poor cows! This dye was made from the dried urine of cows fed nothing but mango leaves. Its production formula was originally kept under wraps, but once its European customers wised up the dye fell out of favor.

Indian Yellow

Slightly redder in hue than Jupiter, but similarly low saturation. Its cloud banding, moreover, shows less contrast than Jupiter’s. Saturn is al-Zuhal in Arabic, from the root for “lagging” as it orbits slowly.

Saturn

Of the New World camelids, the others being the llama, guanaco, and alpaca, this is the smallest. Vicuñas bear the finest and softest wool legally available (at $400 to $600 per kilo) and their populations are now sustainable thanks to the heroic conservation efforts of Peru, Argentina, Bolivia, and Chile.

Vicuña

Aside from gold and copper, the only other metallic element showing any color when pure is cesium. It’s also unusual in being liquid at ordinary temperatures, though it does need to be fairly warm, 28.5° C (83.3° F) to melt. It’s also dangerously reactive, especially in the presence of water.

Cesium

Derived from certain Asian trees and often used to dye monks’ saffron robes. It’s also a powerful laxative and diuretic which, in the form of Dr. Morison’s Vegetable Pills, resulted in his 1836 conviction of manslaughter over a customer who died from them.

Gamboge

Jupiter’s riotously colored cloud bands average out to a beige. Some of Jupiter’s satellites are so far out from it that their orbits’ widths take up 4 degrees of the sky as viewed from Earth — 8 times the width of the moon.

Jupiter

Physician/Chemist Edward Bancroft (1744–1821) invented this pigment during the 1780s. It comes from Oak bark. The active brilliant yellow compound, Quercetin, occurs also in various fruits and vegetables and in capsules as dietary supplements.

Quercitron

The light tan average color of over 200,000 galaxies according to a Johns Hopkins University study in 2002. Many of their stars are white, a few are bluer, and the majority tend to be small and red. This averages out as a reddish off-white.

Cosmic Latte

An inorganic pigment, niobium sulfur tin zinc oxide; supremely stable, opaque, and lightfast both to visible and UV; 90% reflective at its hue (640-700 nm); developed by Boocock, Smith, and Trojan for the Shepherd Color Company in 2010 and patented in 2015

NTP Yellow

A brilliant arsenic sulfide pigment related to Realgar (q.v.). During the Roman period Orpiment typically wound up in the beeswax used in writing tablets to make the letters easier to see.

Orpiment

The most reflective planet at 70%, very slightly yellowish with solid cloud cover in visible light. That overcast traps heat so well that daytime and nighttime temperatures on the ground are nearly the same: 474°C or 890°F.

Venus

A close-in moon of Saturn and the solar system’s most reflective known object. Enceladus is covered with water ice constantly freshened by its tidally driven cryo-volcanoes.

Enceladus

Many wince when the subject of cadmium is brought up, though its chief hazard lies with the inhalation of cadmium-pigmented chalk dust. The yellow is cadmium sulfide, a safer and more lightfast replacement for the mercury sulfide of Vermilion.

Cadmium Yellow

Yes, the planet Mercury is quite dark — bright, though, when viewed alone in space. Its magnetic field interacts with solar wind to generate “tornados” on its surface. (Black shown lower left corner for comparison.)

Mercury

Incredibly, our red cones actually peak at the greenish yellow part of the spectrum. Our brains extrapolate that to red. The ability to perceive oranges and reds is a survival benefit as many fruits display those colors to signal they’re ready to eat.

Red Cone

This was a copper arsenite product that found use in paints, clothing, printing, candles, and toys. Extremely popular, extremely poisonous. Green-loving Napoleon’s rooms on St. Helena were saturated with Scheele’s Green, which may have contributed to his death of stomach cancer at 51.

Scheele’s Green

Named after the liqueur produced by the Carthusian monks of Grande Chartreuse, France, using no fewer than 130 different plant ingredients. It was originally intended as a medicine. (And yes, Carthusians, Trappists, and the like are allowed to speak. They just keep it to a minimum.)

Chartreuse

The spectral area our green cones center on

Green Cone

John Deere founded this company in Grand Detour, Illinois in 1837. The distinctive green with yellow trim crept in between 1890 and 1910 on its products, but the logo itself didn’t adopt them until 2000. The original 1876 logo, by the way, featured a deer that lives only in Africa.

John Deere Green

The classical Chinese and Korean jade-green pottery that originated with the Song Dynasty (960–1270 CE). The article was coated with an iron-rich clay slip and fired in an oxygen-poor environment. It was a difficult art to pull off successfully. Celadon — a European appelation — was a character in L’Astrée by Honoré d'Urfé, a 17th century French novel extolling bucolic tranquility.

Celadon

Also known as terre verte, a highly stable hydrated iron potassium silicate mineral pigment that has been detected in Roman frescoes. Tavush Green occurs in deep oceanic deposits or deeply buried in dry land that was once oceanic.

Tavush Green

This is the peak wavelength of light that the sun radiates. It looks white overall, though, because enough of the visible spectrum on either side of this green hue gets added in. Astronomers classify the sun as a “yellow” star, largely through tradition.

The Sun(?)

The maximum spectral sensitivity of the rods in our retinas, which allow us to see monochromatically in dim light. Yet some experiments now suggest rods contribute to daytime color discrimination also.

Rod

Smaragdine is actually an English word meaning “pertaining to emeralds.” This particular shade — green leaning slightly toward cyan and as saturated as possible — represents the ideal color for the highest-quality emerald.

Smaragdine

Botanical artist William J. Hooker (1779–1832) produced this with Prussian Blue and Gamboge. The latter pigment faded with sunlight, though, so nowadays Hooker’s Green is manufactured with more modern compounds.

Hooker’s Green

A copper bismuth arsenate pigment, soft, brittle, and rare. Widely reported to have been discovered in 1879 by mining engineer Anton Mixa, hence its name. But then again, we know Giotto used it.

Mixite

For centuries this was the most vibrant cyan easily accessible to artists. Workers would hang copper plates over boiling vinegar and then scrape off the resulting copper acetate crust. Copper-rich statuary left outdoors, such as the Statue of Liberty, develops Verdigris patina.

Verdigris

A bit bluer and darker than Uranus. Its atmosphere is similarly methane-based, but its winds blow the fastest in the solar system at up to 1200 miles per hour. Like the other gas giants, Neptune gives off more heat than it receives.

Neptune

The legendary color from Coventry’s medieval weaving trade now adorns its flag. We know that woad, a local plant of the cabbage family, and water from the River Sherbourne were involved. But beyond that, Coventry Blue’s formula is lost.

Coventry Blue

Blue oceans predominate, plus green and brown landscape. Clouds and polar ice simply boost the earth’s overall brightness without affecting the hue. Our planet is receding from the sun at a little over half an inch per year.

Earth

The Pre-Columbian Mesoamericans’ solution to the blue challenge: indigo from New World vegetation and a type of fuller’s earth, palygorskite, they might have had to import. Maya Blue’s secrets had died out by the early 1800s but have recently been solved chemically by a US company.

Maya Blue

Its methane atmosphere absorbs red light and reflects a cyan tint. Uranus is 14.5 times as massive as the earth but, if its surface were solid, its gravity would be slightly less than ours.

Uranus

Early synthetic pigment manufactured from an iron mining byproduct, iron ferrocyanide, first sold as an artists’ color. It’s also an active compound in laundry bluing that’s indispensable for the crystal “rock gardens” of any proper childhood. (I still remember that wonderful smell.)

Prussian Blue

William Payne (1760-1830) was a painter best known for his watercolors and his signature pigment combination, Payne’s Gray. While never strictly standardized, a blue (Ultra­marine or Prus­sian Blue), a tan (Raw Sienna or Ocre), and a touch of red (Cochineal) are often quoted. The result is a low-saturation blue.

Payne’s Gray

This is shellfish-derived Tyrian Purple (q.v.) but with one of its bromine atoms knocked out. We now know the Tekhelet of the Hebrew Bible and Jewish tradition, used anciently to dye tassels affixed to the corners of ceremonial cloths, was Royal Blue.

Royal Blue

Named from a Latin term for India, its source, and used originally for blue jeans, indigo comes from a plant of the pea family. Like Indigo B, chemically similar to Tyrian Purple and Royal Blue.

Indigo A

An ultra-pale blue named after Teddy Roosevelt’s daughter Alice Roosevelt Longworth (1884-1980) and applied to the USS Theodore Roosevelt. Inspired hit song “Alice Blue Gown” and Broadway musical “Irene,” made into a 1940 film starring Ray Milland.

Alice Blue

This is a finely pulverized cobalt oxide-doped glass, used historically as a price-cutting substitute for Ultramarine and especially fashionable during the 17th century.

Smalt

I took a tour through the Delft factory during high school. This is the color most typically associated with the hand-painted patterns on their tin-glazed pottery, a cobalt blue (CoAl2O4) dating back at least to the 1600s. Delftware is one of the few highly prestigious yet artisanal products you can get for a reasonable price.

Delft Blue

Those notorious radium clock dials typically used a green-fluorescing phosphor, but pure radium metal itself is noticeably warm and glows gently bluish on its own. It’s easy to see how Marie and Pierre Curie were so transfixed by it. In the fullness of time it would kill her, though Pierre would escape that fate when he died from a road accident in 1906.

Radium Glow

This was the world’s first synthetic pigment, a fired calcium copper silicate complex developed by ancient Egyptians and essentially identical to their blue faience. Oldest known samples date from ca. 3250 BCE. Its popularity extended through classical times but the secrets of its formulation died out the 4th century.

Egyptian Blue

An oxide of yttrium, indium, and manganese, the first highly stable, strongly blue pigment discovered in 200 years. It’s now available to artists at around $7 per gram. Professor Mas Subramanian and Andrew E. Smith discovered it accidentally in 2009 at Oregon State University, where my cousin had taught music.

YInMn Blue

The bluest star known, Alnitak is a very hot (30,000 K) blue supergiant, one of the three main stars in Orion’s belt. In Chinese it’s correspondingly Shēn Xiù yī (First of Three Stars). It’s 1262 light-years away.

Alnitak

Meaning “intrinsic gray,” this is the color German physicist Gustav Theodor Fechner (1801-1887) reported to be what human vision perceives in darkness with eyes closed. Due to the visual noise from the rods and cones, it’s bluish and slightly brighter than total black (lower left corner for comparison).

Eigengrau

This is a GAS, trifluoronitrosomethane, with a freakishly deep blue color. It would be a laugh riot for parties but for (1) its awful smell and (2) its sufficient toxicity to have been considered for chemical warfare. It’s used to make certain types of rubber.

CF3NO

Ground lapis lazuli, historically the rarest and most expensive pigment. Raphael, Leonardo da Vinci and Michelangelo used Ultramarine when they could afford it. In 1828 Jean Baptiste Guimet earned a prize for his synthesized version, which immediately dropped Ultramarine’s price to a tenth of what it was.

Ultramarine

This is the hue the blue cones in our retinas are most sensitive to.

Blue Cone

This ancient synthetic pigment, a barium copper silicate with copper oxide, is some 2800 years old but its arcane process wasn’t successfully replicated until 1992. Han Purple appears on the terracotta warriors of Qin Shi Huang, though due to its peculiar properties might, amazingly, find use in quantum computing.

Han Purple

Certain bacteria produce this striking dye naturally. Due to Violacein’s anti-bacterial, anti-viral, anti-fungal and anti-tumor properties, genetic engineers are hard at work developing ways to produce it industrially for medicines, cosmetics, and textiles.

Violacein

Widely known only since 1978, Charoite is an exceedingly rare silicate confined to a tiny minerological zone in Siberia’s Sakha Republic. Its first samples investigated, with their wildly swirling bright purple patterns, were assumed artificial. Named from the Russian verb charobat’ (to charm or bewitch).

Charoite

This is the purplish version of indigo dye, which can vary in hue depending on the specific indigofera species used and its processing method. Like Indigo A, chemically similar to Tyrian Purple and Royal Blue.

Indigo B

Ammonium manganese III pyrophosphate, introduced from Germany in 1688. As a paint it doesn’t cover very well, but Claude Monet exploited it effectively for his shadows. It also shows up these days in cosmetics.

Manganese Violet

History’s first synthetic dye was discovered accidentally by 18-year-old chemistry student William Perkin in 1856 while attempting to synthesize quinine to treat malaria. From Mauve, his company would go on to add and market Analine Red, Analine Black, and Alizerin.

Mauve

A synthetic dye patented in 1859 by François-Emmanuel Verguin and named to honor the Battle of Magenta fought between the French/ Sardinians and the Austrians on June 4, 1859, near the town of Magenta in Lombardy. Final score: F-S 1, Austrians 0.

Magenta

As was Magenta (q.v.), this one was named after a battle. Part of the Second Italian War of Independence, this one took place on 24 June 1859 when the Italo-French forces captured an Austrian fortress.

Solferino

A natural, deep magenta alcohol-soluble dye derived from the root of dyer’s alkanet (Alkanna tinctoria) and exploited since ancient times for decoration, cosmetics, and food such as the curry dish rogan josh.

Alkanet

A classical miracle derived from certain Mediterranean snails, highly stable over time unlike most ancient dyes and always spectacularly expensive. Sumptuary laws often prohibited Tyrian Purple being worn by any but the highest and mightiest. Named after the Phoenician city of Tyre.

Tyrian Purple

Stuart Semple, who invents and markets outrageously unusual paints, simply calls this one “The Pinkest Pink.” It’s fluorescent, which means it converts other wavelengths to emit more of certain colors than it actually receives. What you’re seeing here is an approximation, as monitors can’t reproduce this color as it really is.

Semple’s Pink

Introduced in 1758 by Dr. Cuthbert Gordon (it’s named after him) who processed it from orchil lichens in the strictest secrecy with a 10-foot-high wall surrounding the plant in Glascow, Scotland. The dye, though, had also been known in classical times.

Cudbear

This dates back to ca. 1875. Treat lapis lazuli with either ammonium chloride or anhydrous hydrochloric acid gas at high temperatures. Some table salt results, which you rinse away, and you’re left with this lovely purplish pigment. Few artists use it, though.

Ultramarine Red

The pink ink of song and fame, the difference between grab-bag clutter and something to store in a vault, seen on a tiny percentage of 3-cent US postage stamps from the Civil War era. This sample is only an estimation from photos, though, so don’t consider it authoritative!

Pigeon Blood

Also known as Baker-Miller Pink, developed to calm violent prisoners in jails. A researcher who studied it, Dr. Alexander Schauss, remarked, “It’s a tranquilizing color that saps your energy. Even the color-blind are tranquilized by pink rooms.”

Drunk Tank Pink

Gold nanoparticles plus tin oxide. Particle sizes ranging from 40nm to 900nm yield the color series shown left to right. In its bright red phase, Purple of Cassius has been used to make artisanal cranberry glass since at least as far back as the fourth century.

Purple of Cassius

Enormously popular in 18th and 19th century France and a favorite of Marie Antoinette, Puce was named for the color of crushed fleas. It’s also the rarest and mostly highly sought-after tint among antique bottle collectors.

Puce

This is the color of the red amaranth flower, a high-saturation red edging very slightly toward magenta. For those to whom pure mathematical red has always looked slightly orange (your author, for example), Amaranth might be the answer. Dye by that name is also known as FD&C Red No. 2, banned in the US but still legal in the UK for glacé cherries.

Amaranth

Like cochineal but taken from a different insect and named for the kermes oak tree on which they feed. Dates back to the ancient Egyptians and used as currency during the Middle Ages, but ultimately fell from fashion in favor of less saturated but far cheaper Mexican cochineal.

Kermes Red

This classic trademark color found on Hershey’s wrappers triggers a Pavlovian response in all confirmed chocoholics. It premiered in 1902, two years after the first bar. The silver lettering, replacing gold, arrived in 1906.

Hershey Brown

This is [very close to] the proprietary color of Mickey Mouse’s shorts, which totally no one else may legally use. It’s a moderately saturated red, moving very slightly into magenta to keep it from looking too much like orange.

Mickey Moose Red

This color was the toughest to pin down. Puccoon is a deep burgundy dye Native Americans used to process from the roots of several plants. The word itself comes from a term for “red dye” in Powhatan, the Algonquian language spoken by Pocahontas’s people.

Puccoon

Famous dye taken from a Latin American insect when dried and crushed. The British redcoats couldn’t have managed without it. Cochineal also shows up in cosmetics and food, especially candy.

Cochineal

The actual blood color of methemoglobinemia, a rare but now treatable condition of elevated methemoglobin (akin to hemoglobin). Some acquire it, but the “Blue” Fugate clan of rural Kentucky famously carries a recessive gene for MetHb that gives some of them bluish complexions. At least two published novels allude to the Blue Fugates.

Blue Fugate

A rare, purplish brown dye derived in minute quantities from the seed cones of California redwoods, specifically Sequoia sempervirens. Similar in color to puccoon (q.v.), it works beautifully for textiles though it fades from excessive sunlight exposure.

Sequoia