What color is a tree? A sky? A sunset? The answers are obvious at first glance. It turns out that there are many ways people see the world, both within and between cultures.
There are many factors that influence how people perceive and discuss color. These include the biology of our eyes, how our brains process information, and the words we use to describe color categories. There are many ways to be different.
For example, people have three types or cones (light receptors in their eyes that can detect different wavelengths and colors of light). Sometimes, however, a genetic variation may cause one type of cone not to work or make it absent altogether, resulting in altered color vision. Some people are colorblind. Others may be color-blind.
Our sex can play a part in how we perceive colors, as well our age and the color of our eyes. Our perception of color can change depending on where and when we were born, what season it is, and how we feel about it.
To learn more about individual differences in color vision, Knowable Magazine spoke with visual neuroscientist Jenny Bosten of the University of Sussex in England, who wrote about the topic in the 2022 Annual Review of Vision Science. This conversation has been edited to be more concise and clear.
How many colors are in the rainbow?
The rainbow is a continuous spectrum. The visible spectrum is composed of wavelengths that vary between two ends. There are no sharp discontinuities or lines. The human eye can distinguish seven colors within this range. In our culture, however, seven color categories are visible in the rainbow. They are red, orange yellow, green and blue. This is both historical and cultural.
Is that what you taught your own kids, now aged 10 and 5?
I didn’t teach my children anything about color, but I was curious to see what their natural thoughts were about it. My daughter, at 5 years old, asked me if we were going to the blue building. It looked white to her. It was illuminated by a blue sky light. An anecdote I have heard is that children sometimes call the sky blue, but later learn to see it as white. All these possibilities were interesting to me as I was curious to observe them in my children.
Surely most people around the world agree in general about the main, basic colors, like red, yellow and blue. Don’t they?
There are many large datasets that look at color categorization across different cultures. There are many commonalities, and this is what the consensus says. This suggests that there may be biological limitations to how people learn to categorize colors. However, not all cultures have the same number of categories. There is also the possibility that color categories are cultural and that cultures experience a certain amount of evolution in terms of color terms. A language may initially distinguish between two or three colors. However, these categories can become more complex over time.
In some languages, such as old Welsh, there is no distinction between blue and green – they both fall under the “grue” category. In other languages, a distinction is made between two basic color terms for blue: In Russian, it’s siniy for dark blue and goluboy for lighter blue. Are speakers who make this distinction able to perceive colors differently? Is it purely a linguistic thing or a cultural thing? The jury is still out on this.
There was an explosive debate online in 2015 about “The Dress,” and whether it was white and gold or blue and black. Why was it so different?
Scientists became very interested in this particular image, too. There has been a lot research into it. a special edition of the journal is dedicated to the dress. It has been established that the lighting you use to illuminate the dress will affect how you perceive it. People who see it as black and blue see the dress as brightly lit by a yellowish light. People who see it white and gold see it more dimly lit by a bluish, shadowy light. It’s ultimately the brain that makes the decision about the type of illumination on the dress.
But then, the question is: Why do some people think bright yellow is better than dimmer blue? It could be your personal experience with different lighting conditions and which ones you are more familiar with, such as blue LED light or warm sunshine. But it could also be influenced by other factors like, for example, changes that happen to your eyes as you age.
One of the reasons people may see color differently is that their cones might differ. Genetic variations might affect the biology of their light detectors. What are the possible variations?
There are many, many combinations. There are three types of cones. We now know more about the variation in the two types that detect medium and long wavelengths. These are known as the L and M cone types. Each one of these has a photosensitive operator, which is a molecule that changes in shape when light is received. It determines the cell’s wavelength sensitivity. Each opsin gene codes for seven sites that are polymorphic. They can have different letters or DNA. There are seven variants that you can choose from. The total number of variants is huge.
One common variation is red-green blindness. What causes it?
This would be an abnormality in either of the L or M cone types. Dichromacy, which is a severe form of red-green vision deficiency, would mean that you’d either be missing the L or M cones or they’d still be functional but not functional.
Red-green color vision deficiency is also called Daltonism, after John Dalton, the English chemist from the 1790s. It wasn’t super obvious to him that his color vision differed from the majority. He did notice that his descriptions of color were different from those of others around him, but these observations were shared with his brother. He believed it was due to an extra filter in the eye. But then, many years later, others were able to sequence his DNA and they could show that he was a dichromat.
In the mild form of anomalous trichromacy you would still have two different cone types but they would be more similar in terms of the wavelengths that they are optimized for detecting than they are normal. The perceived differences between red-green would be reduced.
What does the world look to those with more severe cases?
A dichromat is essentially blind to a whole axis in color vision. Their color vision becomes one-dimensional. It’s difficult to describe how it looks because we don’t know what the two poles of this dimension are subjectively. The axis between lime green and violets in a normal color space is preserved. This is how it’s often presented. It could be any of the hues that are perceived. We don’t know.
There are cases in which people have been monochromatic in one eye. You can ask them to match the colors they see with the normal, trichromatic eyes. Sometimes they see more with the dichromatic eyes than we expect. We don’t know if this is typical for a regular dichromate who doesn’t have a trichromatic eye to wire up their brain.
Do these deviations from the norm make the world less colorful? Can some genetic variations actually improve color perception?
Anomalous trichomacy is an interesting case. The majority of the time, color discrimination is very low. However, their cones are sensitive to different wavelengths and can discriminate certain colors in some cases. It’s called observer metamerism.
Then there’s Tetrachromacy. This is where someone with two X-chromosomes has instructions for both an altered and regular cone. It gives them four types of cones. This is what we know. We don’t know if they can use the extra cone type to see colors that normal trichromats cannot see or can’t distinguish.
The strongest evidence comes from a test where observers had to make a mixture of red and green light match a yellow; some individuals couldn’t find any mixture that would match the yellow. They would need three colors to mix together in order to make a match. It’s almost as if they have four primary colors instead of the usual 3. It’s difficult to prove why this is happening or what they see.
Do these people have color super-vision,
We didn’t ask women to tell us their color vision status. More than 50 percent of women have four cone types. Two of these cone types are usually very different so it may not be enough for tetrachromatic vision.
Because your subjective perception of color is so personal, it can be difficult to compare your vision to others. John Dalton was the first person to identify red-green color blindness, in 1798–that’s really quite recent. He was a severe type. He was not able to see the whole picture.
Are there any biological differences that can affect color vision beyond genes?
Yes. The lens yellows with age, especially after the age of 40, and that reduces the amount of blue light that reaches the retina. The macular pigment also absorbs short wavelengths of blue light. Different people have different levels of this depending on what they eat. The thicker the pigment, the more lutein and/or zeaxanthin you consume, substances that come mainly from vegetables, such as leafy greens. The Iris color may also have a correlation with color discrimination. It could play a role in determining how vivid your experience of color is. Tests of color discrimination show that people with blue eyes do slightly better than those with brown eyes.
Is color perception affected by the environment around us? To put it another way, if I grew up in a yellow desert or a green jungle, would my ability to distinguish between different colors in these regions of the rainbow affect my color perception?
Yes, it can. This is a very hot topic in color science research. For example, whether there’s a separate word for green and blue seems to depend, in part, on a culture’s proximity to large bodies of water, for example. This is a linguistic thing, and we don’t know if it affects their actual perception.
There is also a seasonal effect that yellow perception has on people. There was a study in York, which is quite gray and gloomy in the winter and nice and green in the summer, and they found that the wavelength that people perceived as pure yellow shifted with the season–only by a small amount, but still a measurable amount.
And there’s also been an effect observed from the season of your birth, especially if you were born in the Arctic Circle. This is likely due to the color of light you are exposed to during your visual developmental.
The environment’s effect on perception can be opposite. While different environments can lead to perception differences, a shared environment can counteract biological differences and make perceptions more similar.
Wow. There are so many differences that it is difficult to understand and determine if they are biological or cultural. It makes it difficult to answer the philosophical question: Is blue the same as your blue?
Yes. I have always considered color fascinating, especially the subjective experience. It’s still a mystery how the brain creates color. It was something I had always wondered about, even before I decided to pursue the topic academically.
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