Color Blindness

The visual condition that changes what colors you see.

To start, being color blind almost never means someone is blind to color, as if they’re living in a black & white movie. “Color blind” usually just means someone doesn’t see the full spectrum of colors like the rest of us. To understand color blindness we have to understand two concepts: light and our eyes.

Let there be light

The colors that we see are photons moving at different wavelengths/frequencies. They’re part of the electromagnetic spectrum. The full electromagnetic spectrum ranges from Gamma rays (the shortest, highest frequency waves – quite dangerous) to radio waves (the longest, lowest frequency waves – not so dangerous). What we call visible light is radiation in a particular range of wavelengths. Within this bandwidth the colors of violet and blue have the shortest wavelengths while oranges and reds have the longest. Through evolution we have developed two small biological machines capable of detecting this range of wavelengths … our eyes.

the electromagnetic spectrum
The electromagnetic spectrum ranges from gamma rays to radio waves, photons moving at a variety of wavelengths & frequencies.

Doctor My Eyes

Our retinas have two kinds of photoreceptive cells: rods and cones. Rods see light & dark while cones see color. We have about 120 million rods per eye and but only 6-7 million cones per eye. Instead of just one kind of cone cell we have three and each kind is tuned to a certain range of wavelengths (short, medium, and long). To put it another way, our three kinds of cone cells are each tuned to see certain ranges of colors – blues (short), greens (medium), reds (long).

Bringing it all together, color blindness is when one (or more) of your cone cell types are either defective or missing entirely. The result is that you are unable to properly see certain wavelengths of colors.

Color Blindness

Why does color blindness happen? While color blindness can be an acquired condition most of the time it’s genetic. The most common forms of color blindness are carried on the X chromosome and because men only have one X chromosome, if it’s defective they’re out of luck. This is why men are more commonly color blind than women. Women have two X chromosomes so a functioning X chromosome will compensate for a defective one. As a result around 8% of men are color blind compared to only around 0.5% of women. That said color blindness isn’t evenly distributed across men – it has a higher prevalence amongst Caucasian men than other ethnicities.

red-green color blindness is the most common form of color blindness
Red-green color blindness is a group of different kinds of color blindness. It’s the most common form of color blindness.

Because cones come in three varieties, and those cones can be defective or absent, the various combinations of factors means there are many forms of color blindness. The most common type is “red-green” color blind (which is a few kinds grouped together) where reds and greens aren’t seen properly and shift to look more like yellows and browns. This is the result of the medium and long (green and red) cone cells being defective or absent. Red-green color blindness accounts for about 99% of all color blindness with about 1 in 12 men and 1 in 200 women having it.

Blue-yellow color blindness is where blues and greens aren’t seen properly. It’s also genetic but it’s not carried on the X chromosome so men and women are affected relatively evenly. It’s quite rare – around 0.01% of men and women are blue-yellow color blind.

Are you seeing what I’m seeing?

The effects of color blindness range from the benign to the dangerous. Accidentally wearing clothes that don’t match can be embarrassing but confusing “stop” for “go” on a traffic light can be dangerous. Color blind individuals can have difficulty determining the ripeness of fruits & vegetables. They can see sports jerseys as similar and have difficulty tracking games. The designer shorthand that red means error/bad while green means success/good (the traffic light analogy) can make a variety of safety features, dashboards, and websites more difficult to use. One positive is that color blind individuals may be better at detecting camouflage.

What do other animals see?

The concept of “color blindness” is relative. What most humans consider normal is not what most bees would consider normal, or dogs, or any other species. So when people say that most other animals are color blind, it’s just that they can’t see the same spectrum of colors that humans normally see.

To start, most mammals are red-green color blind (which to them is normal). They tend to only have two cone cell types, lacking the third we have to see a wider range of colors. So when a dog can’t find the green tennis ball in the green grass, it’s probably because they really can’t see it (especially if it has stopped rolling). Dogs rely on movement to distinguish between things more than we do. That said dogs have more rods than humans so when it seems like they’re looking at something in the dark, and you can’t see anything, they’re probably seeing something beyond your vision.

The old idea that bulls dislike the color red is untrue – they’re red-green color blind. When a matador waves a red/pink cape to attract a bull the bull is responding to the motion of the cape, not the color. Dolphins and other marine animals see even less due to having only the long wavelength cone type and are monochromatic. Deer are red-green color blind but can see more shorter wavelength colors than we can including some amount of ultraviolet which to us is invisible. Some laundry detergents contain brightening agents that are intended to brighten the colors of your clothes but can make clothes look bright blue to deer. The result is that, even if your clothes are camouflaged, the deer probably saw you long before you saw the deer.

Even beyond seeing ultraviolet, some animals can detect/see the Earth’s magnetic fields. It’s believed that robins can see magnetic field lines as a darker shading on the normal colors they already see, but they can only see it through their right eyes and only on clear days. When cryptochrome molecules in their right eyes are struck by blue light the molecules become active and allow robins to see magnetic fields which they can use to navigate as they migrate north & south. Interestingly, non-migratory bird species seem to have less sensitivity to magnetic fields than migratory birds.

Finally, contrary to popular misconception, bats are not blind and some actually have quite decent sight. While they are red-green color blind like most other mammals they have an ultraviolet sensitivity that helps them hunt as well as detect predators. All of this in addition to echolocation means they are quite capable of seeing and navigating the world around them. That said, some species of bats as well as other nocturnal animals have no cones at all and are really truly color blind.

Egyptian Mummies: From Medicine to Paint

For hundreds of years Europeans used ground up Egyptian mummies as medicine and paint pigment.

The Arabic word mūmiyā (which later became “mummia”) was the name for the black sticky asphalt material that came out of the ground used as a sealant, an adhesive, and as medicine around the ancient world. Pliny the Elder and others wrote about the medicinal uses for mummia which became a bit of a cure-all for a range of ailments.

Unfortunately mummia the petroleum product looked like another black substance that was a byproduct of the Egyptian embalming process. As such the word “mummia” came to mean both the petroleum product AND the byproduct of Egyptian mummification, which was then even further confused as meaning an entire mummified body. This is how we got the word “mummy”. Unfortunately this series of mistakes also led to hundreds of years of cannibalism.

Cannibal Medicine

Since the petroleum based mummia was used both externally as a salve as well as ingested internally, the Egyptian mummy version of mummia became used in the same ways. The 11th century physician Constantinus Africanus even described mummia as a “spice” found in the sepulchers of the dead. Soon the human version replaced the petroleum version and people began to crumble & grind human corpses for medicine.

With the Crusades, Europeans learned of mummia and its medicinal possibilities. This significantly increased European demand for Egyptian mummies and by the 15th-16th centuries there was a thriving trade in mummies. Thousands of bodies were being exhumed and shipped to Europe to be turned into medicines. In 1586 English merchant John Sanderson shipped 600 pounds of mummies to London to sell at various apothecaries. This was fueled in part by orientalism, that Egyptian mummies had some sort of exotic ancient knowledge or power.

Europeans would consume portions of Egyptian corpses for help with general pain, ulcers, inflammation, epilepsy, cough, difficult labor, etc. – none of which worked, or if they worked it wasn’t the mummy that was the active ingredient. The practice was so common Shakespeare included mummy as an ingredient in the witches’ potion in Macbeth. Demand was so high that by the 17th century some mummy dealers were producing counterfeit mummies. Newly deceased people, animals, or prisoners who had been purposefully starved & executed, were put through a process to simulate ancient Egyptian mummies.

After a few hundred years of medicinal cannibalism Europeans began to express doubt as to the practice’s efficacy (and ethicality). The 16th century herbalist Leonhard Fuchs felt foreign mummies were acceptable but local ones were wrong. While doubts arose during the Renaissance in the 16th century it took until the 18th century age of Enlightenment for the practice to fall out of fashion. As consuming mummies slowly ended Egyptian mummies took on a new role: paint pigment.

The Egyptian Widow by Lourens Alma Tadema is an 1872 painting of Egyptian life potentially painted using mummy brown paint.
Liberty Leading the People by Eugène Delacroix is another painting that’s theorized to contain mummy brown.

Mummy Brown

Around the end of the 16th century artists began using ground up Egyptian mummies (mixed with other materials) to produce mummy brown, a shade of brown pigment. Apothecaries that were grinding up mummies for medicine began to grind them up for paint as well. As a paint it was good for shadows, flesh tones, and glazing. Artists Benjamin West, Martin Drolling, Lawrence Alma-Tadema, Edward Burne-Jones, Eugène Delacroix, and others all painted with mummy brown.

It wasn’t until the 19th century that mummy brown began to fall out of favor. That said as recently as 1926 C Roberson & Co. still sold mummy brown made with ground up Egyptian corpses. As mummy brown died out so too did hundreds of years of large-scale desecration of deceased Egyptians, using human beings for medicines and paints.

Eye Color

Humans originally had brown eyes until genetic mutations started making variations. No two eyes are identical, not even your own.

The color & patterns of your eyes is as unique as your fingerprints. Several gene variations all contribute to giving each of your eyes a particular design and shade of color (or colors if you’re heterochromatic). No two eyes are identical.

Originally all humans had dark brown eyes (along with dark brown skin) which helped to reflect some of the harsh rays from the sun. As humans migrated out of Africa and up into Europe, where winter sees less sunlight and the land is further away from the direct sunlight of the equator, there was no longer a need for so much protection from the sun’s harmful UV light. This is where the first mutation in human eye color took place. Sometime between 6,000 and 10,000 years ago the first blue-eyed person was born, from which all other blue-eyed people are descendant.

Eye Colors

Our skin and hair is colored using the brown pigmentation called melanin. The back of our irises also contains melanin which gives our eyes color. Melanin is brown, and so brown eyes using brown pigmentation is easy to understand. Light enters the iris, the melanin absorbs some wavelengths of light while reflecting back out the necessary waves to make the color brown, making brown eyes brown.

You would think then that blue eyes use blue pigmentation, but they don’t. Blue eyes use the same brown pigmentation as brown eyes but in lesser quantities. The other trick is that, since eyes are three dimensional, blue eyes absorb and scatter waves of light differently than brown eyes. The longer light wavelengths (reds & oranges) get broken up inside the eye and only the shorter wavelengths (blues) get reflected back out making blue eyes look blue. This scattering effect of allowing/blocking certain wavelengths is also what gives the sky different colors.

Even though all colors of eyes use brown melanin, variations in the construction of the eye and how it absorbs & scatters various light waves makes an iris a certain color.

Brown, blue, gray, hazel, green – all eye colors use some amount of brown melanin combined with various ways of scattering & absorbing light to make whatever color the eyes are. People with albinism can lack the necessary pigmentation to make their irises as opaque as other people’s. Irises that fail to block excessive light from entering the retina can cause a variety of vision problems including extreme sensitivity to bright light.

What does eye color “do”?

As for any potential purpose, eye color doesn’t “do” much. Unlike other genetic traits which evolution embraced because they helped our chances of survival, eye color variations seems to be largely perpetuated through romantic desirability. People find certain eye colors more attractive and so the genes for those colors live on. Your eyesight isn’t any better or worse because of a certain color eyes. Light travels through the pupil to the retina and so the color of the iris doesn’t change what you see. This is why cosmetic contact lenses can change your eye color without changing what you are seeing – they are only covering the iris.

There are some minor effects of having different eye colors. Because of how light is scattered and absorbed inside the eye, lighter colored eyes are sometimes more sensitive to bright light leaving some to squint more as well as needing to wear sunglasses more frequently. Driving at night can also be difficult because the glare from oncoming traffic can be more harsh. People with light colored eyes are more likely to develop macular degeneration, but people with brown eyes are more likely to develop cataracts. Finally in sports, people with lighter colored eyes tend to be better at hand-eye coordinated activities such as throwing, bowling, golfing, pitching, etc. Brown-eyed people tend to be better at the actions where they react such as hitting a ball, boxing, playing defense, etc.

Added info: Getting reliable statistics on eye colors is difficult. That said brown eyes are the most common color type in the world at somewhere between 55-79%. Gray eyes seem to be the rarest at less than 1%. The eyes of some babies start out as blue but eventually become green or brown as their eyes develop more melanin. Few blue-eyed babies will have blue eyes as adults.

Liz Taylor was said to have violet eyes, but in reality she had blue eyes but with a genetic mutation to have double eyelashes which made her eyes look more purple. David Bowie was known for having two different colored eyes, but this was also an illusion. When he was 15 he got in a fight over a girl and his left eye was damaged leaving the pupil permanently dilated. This gave the impression that he had one black eye and one blue eye, but in reality both of his eyes were blue.

Liz Taylor and David Bowie both had remarkable eyes.

Autumn Colors

Leaves change colors in autumn because the temperature drops and the hours of sunlight diminish.

The leaves of deciduous plants change color as summer ends and autumn begins. Cooler temperatures and fewer hours of sunlight trigger chain reactions in how plants operate. When leaves are green it’s because of an abundance of chlorophyll which absorbs sunlight and produces simple sugars to feed the plant. Autumn’s seasonal changes tell plants to produce less chlorophyll. Autumn also tells plants to start producing special corking cells at the base of each leaf stem. These cells reduce the flow of nutrients (including chlorophyll) into or out of the leaves and eventually completely seals off the leaves from the branches allowing them to fall off.

So as chlorophyll production decreases, and leaves become sealed off from the rest of the plant, leaves can no longer stay as green as they were. What color they become depends on the plant.

Yellows and Oranges

Chlorophyll is the big green machine, it outweighs all other chemicals present in a leaf. As there is less and less chlorophyll present, the carotenoids that have been present the whole time begin to be visible. These chemicals give leaves different shades of yellow and orange depending on the plant. Carotenoids are also what make carrots orange.


Unlike carotenoids which are present in leaves all year, anthocyanins are pigments specially produced just for autumn. The end of summer triggers the production of anthocyanins which give leaves the deeper colors of reds, purples, and even blacks. Anthocyanins also are what give cranberries, cherries, and blueberries their colors.

Top Down

Much like a corporation, change takes place from the top down. Higher elevations see leaves change colors earlier than lower elevations. This is because higher elevations reach the cooler temperatures necessary to trigger the change before the same plants in lower elevations which have warmer temperatures.

A tree turning color from the top down.

Change also takes place top down in another way. The top leaves of a plant will typically begin changing color before the bottom leaves. This is because the top leaves are furthest from the roots and, since it takes more effort to send chlorophyll to the top of a plant, the top leaves will start losing their green color first.

“Autumn is a second spring when every leaf is a flower.” ― Albert Camus

Orange the fruit, orange the color

Orange the color was named for orange the fruit, not the other way around.

The English word for the color orange has a trail back through a few European languages but has its origins in the Sanskrit “nāraṅga” which was the name for the orange tree. Oranges the fruit came to Europe through Spain with the Moors, who in Arabic called the fruit “nāranj”.

From the Arabic name for the fruit, “nāranj” became “narange” in English in the 14th century and by sometime in the early 16th century the spelling became “orange”, and was then used to describe things that were the color of the fruit.

Some confusion may apply

Without a name for a color, cultures use the words they do have to describe the things around them. Because English didn’t have a word for the color orange until the 16th century, some things that are orange (or orange-ish) were labeled as red because it was the closest color that English had a word for. “Red” hair and the robin “redbreast” for example are really more orange than red, but they were named before English had the word “orange”.

Describing the colors of things before a language has names for those colors had been a problem across cultures for a long time. The Ancient Greeks had a very limited palette of color names to choose from. For example, there seems to have been no word in Ancient Greek for the color “blue” so in Homer’s The Iliad and The Odyssey he describes both the sky and the sea as being a wine / bronze color. Even stranger, he also describes sheep as being wine colored.