Is your green the same as my green?

Here is a common question when I give a class on color theory: "Do we all see color the same way?"

Often the question starts with the words "My wife...", or "My husband..."  There is, at the very least, a perception that men and women see color differently. But what about me and some other guy? Do we see color the same?

There are lots of answers to this question: How much variability is there is color perception? That makes it fun to blog about!

High level evidence of gender differences

There is a well known anecdote that if you ask a guy about his car, he will give a lengthy discourse about the engine. A woman will tell you the color. If you can get a guy to mention the color of his car at all, he will use basic color names like "green" or "blue". A woman will use a nuanced color name like cerulean or mauve to describe her car.

My wife and I, discussing automotive colors

I am not aware of any experimental evidence of gender bias in car automotive descriptive preference, but I know of a brilliant study from a brilliant color researcher [1]. He provided some evidence that somewhere between a photon entering the eye and a neuron recalling a word, there is some difference in the way men and women perceive color. This incredibly smart and good-looking color scientist asked 50 people to write down all the single word color names that they could think of in two minutes. Here is his conclusion:

"There was a statistically significant difference between the number of colors that the men could recall versus the number that the women could recall. Men averaged 15, and women averaged 18."

(A bit more on this groundbreaking experiment can be found in the section "Eleven" in the blog post "How many colors are in your rainbow?")

Where does this happen? Is this in the physiology of the eyes? Or maybe it's a brain thing -- woman are, on average, better at verbal skills than men? Or is it a cultural bias because women in general are encouraged to be interested in fashion?

Let's consider the differences in physiology...

Color blindness

Color blindness is one explanation I have heard for why there is a gender difference in color perception. Men are more likely to be colorblind than women. Dogs are colorblind. Therefore men are more likely to be dogs than women.

Comparison of how I see apples, and how my colorblind dog sees apples

It's true that women are less likely to be colorblind. Color blindness is a sex-linked trait [2]. The weakness is something expressed on the X chromosome. Basically, you need to have one copy of the color vision genes on either chromosome to have full color vision. Since women have two X chromosomes, they have two chances to get all the pieces for color vision. Men, who only have one X chromosome, only have one shot. As a result, color blindness is more prevalent in men than in women. About one man in a dozen is colorblind. For women, it's about one in 200. [3]

As I said, this is true, but it's not an explanation for why there is a gender difference in the color naming experiment. Even with the elimination of any possible colorblind men from the experiment, the results were still statistically significant. And what about the 11 out of 12 men with normal color vision who still prefer to talk horsepower and miles per gallon?

Tetrachromacy

As I described in Organizing your crayons, color is three-dimensional. The reason for that is simple. We have three types of cones (light receptors) in our eye. Each cone responds to a different range of wavelengths. These three cones are called "L" (which stands for red), "M" (which stands for green), and "S" (which stands for blue). [4]

There is some controversy on this, but there are reportedly a number of people who have four different types of cones. To them, color is four-dimensional. 

Just to give a feel for what that means, it is a rough approximation that each cone allows us to distinguish about a hundred levels. For a combination of two cones, it is possible to distinguish 100 X 100 different colors. (For those who don't have a calculator handy, that number is 10,000, or ten thousand.) This is a rough idea of the number of colors that a dichromat (someone who is color blind with two types of cones) can see. 

For most of the population, there are three types of cones, so there are 100 X 100 X 100 different combinations that could be distinguished; one million perceptible shades of color.

A tetrachromat has four different types of cones. As a result, there are one hundred times as many different shades of color that this person could distinguish. One hundred million colors. Such a person could sense subtle differences in hue that I could only see with the help of LSD. Imagine how long it would take such a person to match their socks in the morning! [5]

Some folk's eyes are just more colorful than others

This is all pretty new research, but by one estimate, only a few percent of the female population (and none of the male population) has this super-human ability. This estimate came from a researcher who used to be right here in Milwaukee by the name of Jay Neitz.

Always wanting to make significant contributions to science, I did a little research on my own on the prevalence of this anomaly. I stopped a hundred woman in the mall and asked them if they were tetrachromats. Unfortunately, I had to curtail my data gathering when the police showed up.

As I have said, the existence of people like this is still under debate. As near as I can tell, the argument against goes something like this: "People who claim to be tetrachromats are just people looking for attention. If the whole tetrachromat thing didn't come up, they would claim to have been abducted by aliens, or would be singing Justin Beiber songs at a karaoke bar." Scary stuff indeed.

But... this still doesn't answer the question of why there is an apparent difference in the way men and two women see color. A few per cent of the female population is not enough to allow all women to be able to point to a color and tell whether it is ecru or oyster.

Physical variation in the eyeball

I just received a copy of the PhD thesis from a fellow by the name of Abhijit Sarkar [6]. The first comment I want to make--and this applies to everyone who is now working on a PhD thesis--is this: Why do you gotta make those things so darn long? And why do you gotta use such big words? I'm just saying... if you want your thesis to be tweeted about, you need to shrink it down to like two or three pages tops. And cut out all those darn equations, ok?

Dr. Sarkar describes several mechanisms within the eye that could cause two people to see color differently. The simplest one to describe is the yellowing of the lens in our eye. This happens gradually as we age. This yellowing has the effect of subduing the effect of light at the blue end.

I see the equivalent of this effect every day. My wife has our bedroom painted a pale lavender color. On a sunny day when the shades are open, the ceiling is a delicate pastel lavender. At nighttime, though, when we view the ceiling under incandescent light, the color is more of a gray [7].

The effect of a yellow filter on purple flowers

The yellowing of the lens in our eye has a similar effect. This effect is most striking for colors in the purple family. Sadly, as we grow older, we start to lose some of the subtle shades of purple. When I am old, I will wear purple, but I will need to have a younger woman around to appreciate it. [8].

Dr. Sarkar talks about a number of other mechanisms in the eye that act like filters to change the tint of what we see. His thesis is littered with phrases like "macular pigment optical density function". This of course, limits my ability to understand what he is talking about. But the big idea is that these tinted sunglasses that are built right into our eyes vary from one person to the next.

Luckily, this gentleman's thesis had a very clear and succinct abstract that even I could understand. There are differences in the make up of people's eyes [9] that mean we all see color just a bit differently. This effect, called observer metamerism, is a bummer. In industry, it makes it really darn hard to match colors. One person with "normal color vision" might say two colors match, and another may say they don't.

The whole crux of his thesis is that the problem is potentially solvable. His research says that people can be grouped into eight categories for their color vision, and he has developed a relatively simple test to categorize them. [10]

The practical application of Dr. Sarkar's work is when you are trying to match a color on a computer monitor with the color of a physical object held next to that monitor. Doing this is common in the printing industry, where people display what is called a proof on a computer screen. Customers sign off on a color based on this "soft proof", and press operators use that soft proof as a reference for when they are printing.

If you knew which category an observer fell into, it would be possible to adjust the computer monitor accordingly. There are some holes in implementation of this. In particular, I am not sure what happens when you have two people from different categories looking at the same screen.

But none of this sheds any light on gender differences. There is nothing in the thesis that is gender specific.

Conclusion

I don't have a final pronouncement on this, but I have yet to find a physiological explanation for why men and women seem to think about color differently. Until I hear differently, I am going to assume that if such a difference really exists, then periwinkle and wisteria and orchid and lavender originate somewhere in the murky canescent matter of my wife's brain, and not in the gray matter of my brain.

As for the simpler question, is there variability in the color response to different eyes, the answer is most certainly "yes".

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[1] When I say something like "brilliant study from a brilliant color researcher", it is generally a euphemism for "I did this work". I prefer the euphemism because I am far too modest to take credit for it.

[2] I am not aware of any research that goes into how often color blind people get lucky, so I would prefer to call color blindness a "gender-linked trait" rather than "sex-linked".  On the other hand, there is a certain blue pill that is taken by some (often older) men that may cause a temporary color deficiency, and use of this blue pill is strongly correlated with getting lucky. I have heard of this pill, but have no personal experience to verify the effect. 

[3] That whole X/Y chromosome thing is a rip off, if you ask me. Men are also more likely to have hemophilia and male pattern baldness. I would give my manhood for another X chromosome!

[4] Ok... LMS stands for long, medium, and short, referring to the range of wavelengths that each accepts. It  is a simplification to call them red, green, and blue, since they are not exactly in the red, green, and blue region of the spectrum. The S cone is close to what we would call blue, but the M cone is broader than just the green part of the spectrum. And that darn L cone overlaps just a whole lot with the M cone. It would not be such an awful faux pas to call this the yellow-green cone. 

[5] If sock matching is an onerous burden for your lifestyle, I recommend checking out this iPhone app for sock matching.

[6] "Identification and Assignment of Colorimetric Observer Categories and Their Applications in Color and Vision Sciences", 2011 from Ecole polytechnique de l’Université de Nantes.

[7] Of course my wife keeps insisting that the color is neither lavender nor gray, but rather a grayish lavender.

[8] My wife objected to this statement. But I won't tell you which one of us is older.

[9] Just to be clear, he is not talking about makeup, as in eye shadow and mascara. He is talking about how the eye is built.

[10] In my own experience, there are two categories of people: those who like to be put in categories, and those who don't.

Organizing your crayons

My little buddy here is intent on an important task. He is trying to organize his crayons.

Go ahead, make my gray!

You may think this is an easy task, organizing crayons, but you would be wrong. At least, that is, if you are an adult. I distributed crayons to a group of first and second graders. I set them loose in a gym and asked them to organize themselves by color. It took maybe ten or fifteen minutes, but they did it. I gave the same task to a group of managers in a large corporation that shall go nameless. They held preliminary meetings with action items for subcommittees to perform market analysis, develop a business case, and research environmental impacts. Project leaders were appointed to develop realistic estimates of timelines, and to do risk analysis. I expect them to get back to me  by mid-June with a detailed action plan. They got started back in September of 2007.

Arranging crayons in a line

One possible way to arrange crayons is by the colors of the rainbow. I pulled 13 crayons out of my favorite box of crayons and made a nice lineup which I call the "craynbow" [1]. You can see red, red-orange, orange-red, orange, yellow-orange, orange-yellow, yellow, and so on.

The craynbow

I know this is completely atypical of me, but I sort of told a lie. The last two crayons on the top, the red-violet and violet-red, are not actually in the rainbow. The most startling difference between the rainbow and the craynbow is that the rainbow is two crayons short of a full deck. This is probably obvious, but the additional two crayons form a bridge that allows us to connect the bottom of the craynbow to the top. Thus, the 13 crayons can be laid out in a circle. 

But there are just a few other crayons that didn't make the cut. Most notably, the craynbow is missing white, gray, black, pink, and brown. Also the craynbow does not have a spot for lavender, burnt sienna, periwinkle, or maroon [2]. There are 96 crayons in my box, and 83 of them don't have a spot reserved for them in the craynbow. You don't have to be the sharpest crayon in the shed to see that you can't arrange a box of crayons in a single line in a way that chromatically feels good [3].

Color is three-dimensional

There is a simple reason why we can't put all the colors in a line. Color is three-dimensional. The craynbow looks at just one of those three dimensions of color, that is, the hue. Us color theory guys have two additional attributes that we assign to colors: chroma and lightness.

Showing hue and chroma

Let's start out with those 12 crayons arranged around in a circle. (I don't know what happened to the 13th crayon, by the way. Maybe it fell behind the couch.) What happens if we mix each of those crayons with a little gray, and then with a lot of gray? The results are shown in the really nifty circle below. Feel free to drop the artist an email telling him just how much you like the circle.

This cool drawing took me four hours to draw

Now for the cool part. Any color in this circle can be identified by naming the hue (the original crayon) and the chroma (how far it is from gray). The hue in this circle is the crayon that you started with. The chroma tells us how much gray was mixed in, that is, how rich the color is.

By the way, if you happen to be into analytic geometry, you might realize that hue and chroma are polar coordinates for the color plane. If, on the other hand, you don't really care all that much about anal retentive geometry, then you probably don't care about whether your polars coordinate.

Showing lightness and chroma

This next image demonstrates how lightness (along the up and down axis) combines with chroma (along the right to left axis). All the colors in this image have the same hue, yellow-red (5YR) [4].

A page from the "Munsell HVC Color Charts"
(It took me four hours to put these paint chips in order.)

Along the left edge, we see a scale of colors that go from black up to white, all with just a tiny bit of orange flavoring to them. As we move to the right, there is more and more orange added--that is higher chroma.

Notice that we just don't get all that many shades of orange-black. As you add orange (or yellow) to black, it just has to get lighter. Thus, there is only one shade of orange on the bottom row. On the other hand, you can add orange to white without significantly decreasing its lightness. So, there are four shades of orange in the top row. The most saturated orange is basically still a pretty bright color. Blue and purple work pretty much the opposite way. Adding blue or purple to a pale gray will necessarily make it darker. It is possible to have a very saturated blue or purple that is also very dark.

These three attributes can be put together to create a color tree. The pages (like the one above called 5YR) are bound together at the left edge, and fanned out as shown in the very detailed and elaborate illustration below.

Here is another four hours of my life spent in Photoshop

Such a color tree was devised by Albert Munsell in the early 1900s. It is a testament to his genius and meticulousness that you can still buy a facsimile of this color tree almost a full century later. Not only that, but the guy actually has a blog, despite the fact that he died in 1918. He must be a ghost writer, I guess.

A very attractive model shows the Munsell color tree

Someday I will write a blog post about how this guy Munsell laid the foundation for the ever-popular color space CIELAB, and came to be known as the Father of Color Science. He was also the father of A. E. O. Munsell, who carried on his work. I don't intend to write a blog post about how Albert became the father of A. E. O.  

What this all means

The first message is that you need three dimensions to organize a box of crayons. That's cool, but the more important message is that with the colors organized and quantified like this, it is possible to put a unique identifier on each color. All you need to do is specify the hue, chroma, and lightness, and you can unambiguously label any color. This might not be as romantic as using words like vermilion or aubergine, but it's a darn sight more precise. What young lady wouldn't prefer to hear poetry that scientifically specifies the color of her rosy cheeks?

  

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[1]  A major supercomputer company is developing a computer just to compute all the colors in the universe. The computer will be called the Cray-Ola.

[2]  A ship loaded with red paint collided with a ship loaded with blue paint. All the crew were marooned.

[3] I used to tell my color classes just that you can't arrange your crayons all in a line in a way that made sense. Some smart alec said "Sure you can. Alphabetically!"

[4] I understand that some people might be so silly as to call the color "5YR" by the pedestrian name "orange". Please try not to laugh at them, ok? (My wife told me that I should point out that I'm being sarcastic here.)

John the Math Guy breaks out of the blog, Jan 2013

I have been hiding in my blog for a while, and decided it would be a good idea to get out to see more of the internet. Here are some of the tracks I have left elsewhere.

Labels and Labeling magazine

Adrian Tippets (a good friend who I have never actually met in person) read my blog post called "Layman's Guide to ISO Standards". He liked it so much that he hooked me up with the wonderful folks at Labels and Labeling magazine. One thing led to another, and "ISO comes to in-line color" was born. Here is the summary:

Achieving ISO compliance with an in-line spectrophotometer is a more difficult project than first appears. John Seymour, color expert at QuadTech, lays out the issues.

Munsell blog

I had an interesting interchange of blogs with Jeff Yurek. Jeff writes an entertaining blog with the uber-cool name "dot color". (I wish I could think of names like that.)

The interchange started with "Why does my cyan have the blues?" Jeff Yurek (a close, close friend who I never met) read this post and was obviously totally blown away my the incredible writing style and the vast knowledge that I evinced with my post. Or maybe he was just desperate for a blog post topic? Either way, he summarized my post in his blog post "How does ink thickness change the appearance of printed color?". 

Turn about is fair play, right? I was desperate for a blog post topic and I decided to co-opt ideas from his blog. I came across a post of his about the Seeing red: can color change your spending habits?. I decided to play off this post by doing extensive research into universality of opinions of color gurus on the psychological effect of the color red. I spent nearly a whole hour on the research that went into the post "Red is the color of..."

Jeff and I played ping-pong for a while. He did a post called  "Shopping for a tablet this holiday season? Don’t forget to look at color performance". Many reviews of the various tablets look at display resolution (pixels per inch). He looked at the color gamut of the displays - how many colors can the display produce.

I followed up with Does my dog appreciate my KindleFire display? in which I either looked at a) tablet apps for testing colorblindness, or b) color-blindness in dogs, or c) the gamuts of various tablet devices, or d) my superior color vision over my wife. I'm not sure what the post was really about, but I got many comments on it, so I followed up with Follow up on colorblindness testing.

Well, Munsell makes stuff for testing colorblindness, so this got the attention of Noni Cavalerie, who is the social media-savvy social media person for Munsell. In particular, she handles the Munsell color blog. Noni, of course, is one of my oldest and dearest friends that I have never met. She couldn;t take it anymore, so she asked me to guest blog. Naturally, I took a subject near and dear to my heart - why I am superior to my dog:  Evolution Trichromacy.

In case you are wondering about this vast superiority I have over my dog, it's because he is colorblind, and I have an opposable thumb. If you want to know why evolution favored primates with trichromatic vision (three types of color receptors), you'll have to read the dog blog.  

FlexoGlobal magazine

I posted a blog called Where are my CIELAB knobs?. My dearest friend Laura Hatch, of FlexoGlobal magazine (a friend who I actually did meet once) liked the blog and asked to repost it. I modified it a little (meaning, I took out the silly stuff), and she made it a Where are my CIELAB knobs?.