Posted on 02/03/2025 6:36:50 PM PST by Red Badger
There is something unique about the color purple: Our brain makes it up. So you might just call purple a pigment of our imagination.
It’s also a fascinating example of how the brain creates something beautiful when faced with a systems error.
To understand where purple comes from, we need to know how our eyes and brain work together to perceive color. And that all begins with light.
Light is another term for electromagnetic radiation. Most comes from the sun and travels to Earth in waves. There are many different types of light, which scientists group based on the lengths of those waves. (The wavelength is the distance between one wave peak and the next.) Together, all of those wavelengths make up the electromagnetic spectrum.
Our eyes can’t see most wavelengths, such as the microwaves used to cook food or the ultraviolet light that can burn our skin when we don’t wear sunscreen. We can directly see only a teeny, tiny sliver of the spectrum — just 0.0035 percent! This slice is known as the visible-light spectrum. It spans wavelengths between roughly 350 and 700 nanometers.
The acronym ROYGBIV (pronounced Roy-gee-biv) can be used to remember the order of colors in that visible spectrum: red, orange, yellow, green, blue, indigo and violet. You can see these colors in a rainbow stretching across the sky after a rainstorm or when light shines through a prism. In the visible spectrum, red light has the longest wavelength. Blue and violet are the shortest. Green and yellow sit toward the middle.
Although violet is in the visible spectrum, purple is not. Indeed, violet and purple are not the same color. They look similar, but the way our brain perceives them is very different.
How we see color
Color perception starts in our eyes. The backs of our eyes contain light-sensitive cells called cones. Most people have three types. They’re sometimes called red, green and blue cones because each is most sensitive to one of those colors.
But cones don’t “see” color, notes Zab Johnson. Instead, they detect certain wavelengths of light.
Johnson works at the University of Pennsylvania in Philadelphia. She and other scientists who study how we perceive color prefer to classify cones based on the range of wavelengths they detect: long, mid or short.
So-called red cones detect long wavelengths of light. Green cones respond most strongly to light in the middle of the visible spectrum. Blue cones best detect wavelengths toward the shorter end of the visible spectrum.
When light enters our eyes, the specific combination of cones it activates is like a code. Our brain deciphers that code and then translates it into a color.
Consider light that stimulates long- and mid-wavelength cones but few, if any, short-wavelength cones. Our brain interprets this as orange. When light triggers mostly short-wavelength cones, we see blue or violet. A combination of mid- and short-wavelength cones looks green. Any color within the visible rainbow can be created by a single wavelength of light stimulating a specific combination of cones.
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Notice that the visible spectrum is a gradient. One color gradually shifts into the next. The activity of cones activated by the light also gradually shifts from one type to the next. At the red end of the spectrum, for instance, long-wavelength cones do most of the work. As you move from red to orange, the mid-wavelength cones help more and the long-wavelength cones do less.
In the middle of the rainbow — colors like green and yellow — the mid-wavelength cones are busiest, with help from both long- and short-wavelength cones. At the blue end of the spectrum, short-wavelength cones do most of the work.
But there is no color on the spectrum that’s created by combining long- and short-wavelength cones.
This makes purple a puzzle.
Purple is a mix of red (long) and blue (short) wavelengths. Seeing something that’s purple, such as eggplants or lilacs, stimulates both short- and long-wavelength cones. This confuses the brain. If long-wavelength cones are excited, the color should be red or near to that. If short-wavelength cones are excited, the color should be near to blue.
The problem: Those colors are on opposite ends of the spectrum. How can a color be close to both ends at once?
To cope, the brain improvises. It takes the visible spectrum — usually a straight line — and bends it into a circle. This puts blue and red next to each other.
“Blue and red should be on opposite ends of that linear scale,” Johnson explains. “Yet at some point, blue and red start to come together. And that coming-together point is called purple.”
Our brain now remodels the visible spectrum into a color wheel and pops in a palette of purples — which don’t exist — as a solution to why it’s receiving information from opposite ends of the visible spectrum.
Colors that are part of the visible spectrum are known as spectral colors. It only takes one wavelength of light for our brain to perceive shades of each color. Purple, however, is a nonspectral color. That means it’s made of two wavelengths of light (one long and one short).
This is the difference between violet and purple. Violet is a spectral color — part of the visible spectrum. Purple is a nonspectral color that the brain creates to make sense of confusing information.
Purple thus arises from a unique quirk of how we process light. And it’s a beautiful example of how our brains respond when faced with something out of the norm. But it’s not the only color that deserves our admiration, says Anya Hurlbert.
“All colors are made up by the brain. Full stop,” says this visual scientist at Newcastle University in England. They’re our brain’s way of interpreting signals from our eyes. And they add so much meaning to things we perceive, she says.
“The color of a bruise tells me how old it is. The color of a fruit tells me how ripe it is. The color of a piece of fabric tells me whether it’s been washed many times or it’s fresh off the factory line,” she says. “There’s almost nothing else that starts with something so simple [like a wavelength of light] and ends with something so deep and rich.”
I was ONLY talking about “under standard light”; NOT under different light conditions. Good grief, I DO know what I’m talking about, re painting, paints,and color theory.
What name did Achilles take when he was amount the women? Imponderables.
The examples in the article; the fruits & veggies and the spectrum chart.
Magenta on my computer.
“The examples in the article; the fruits & veggies and the spectrum chart.”
The first is not a specific example. Just a stock photo.
Each monitor is different. Take a photo of your pigment and display it on your monitor. It will look a different color.
‘Wine dark’ (which could also have been written ‘wine faced’) could apparently have been interpreted as meaning something other than color. It could simply have had to do with light and dark.
It’s an interesting problem:
https://en.wikipedia.org/wiki/Wine-dark_sea
Very lovely.
(Are we sure that’s purple, though, and not violet?)
Sweet Dreams :-)
“I was ONLY talking about “under standard light”
Maybe the photo you saw of the veggies was not taken under a standard light.
Maybe the camera taking the photos had sensors not 100% calibrated to the eye.
Maybe the camera imaging processing resulted in color shifts.
Okay, as a painter, I have painted, inside, in the daytime with only light from outside coming in and in the evening, with an overhead light fixture.
I have also done plein air painting, which is a different kind of light, because it is direct sunlight, which may or may not hit the paper and/or the landscape that I'm painting. In plein air, one can and usually does, get up close to the tree, flower, grass, whatever, to check color, textures, minute details ( botanical work is often detail happy! ), so yes, different kinds of light, different times of day/night, but I don't see the difference.
If I mix every color ( though painters usually do NOT do that to get black ) yes, it will come out sort of black, IF I omit Titanium, Buff, and/or Chinese White.
Under NO circumstances, that I work under, can I mix all colors and get white.
And...most watercolorists DO NOT use white paint. If we do, it is NOT the white watercolor; it's Dr. Ph Martin's BLEED PROOF paint. The other way we get white, is to use masking fluid, so that when that substance is removed, the sterile, white paper is exposed. But....since most white things or highlights are NOT pure white, we use a different method, entirely, which is using the MOST watered down paint to differentiate certain portions of the subject, leaving white paper areas exposed.
LOL...probably too much info above and perhaps NOT the answer you were looking for. But it's the best I can do.
Ummmmmmmmmmmmmm...I have taken pictures of some of my paintings and have seen them on my laptop. The colors are the same.
That's true but it's not primarily due to monitor differences.
The pigment exhibits subtractive color. The monitor produces additive color. The two are fundamentally different -- you cannot produce a true (exact match) additive color with subtractive pigments, just as (as you example shows) you cannot produce a true (exact match) subtractive color with additive sources.
You can get REAL close for specific instances, but it's a fundamentally unsolvable problem in the general case.
Do you guys know any optical physics at all, or are you just trolling each other into oblivion? I'm beginning to suspect the latter. :-)
It's a lovely picture!
Thank you for your thoughtful reply.
White pigment paint absorbs no visible wavelengths which is why it not only appears "white", but also why surfaces painted white don't get hot in the sun, whereas surfaces painted black absorb all the visible wavelengths which is why they get hot in the sun.
That is the very definition of "reflective color".
Do see my reply to dayglored #130.
I’m NOT “trolling”; but do think that I am being TROLLED.
Re painting...Except for a certain era and school of art, re Dutch painters, black has not generally used in oil or watercolor painting for centuries. Shadows are usually some form of grey or a much darker color than the subject.
There are exceptions and the granulating blacks, in watercolor, when used very sparingly ( usually added to another color ) is due to granulation. LOL...just some useless but I think interesting info.
Like performing bards down through the ages, he relied on repeated images pad the meter and reduce the sheer amount of memorization. A modern scholar (not even a clue who it was at this point) memorized the Iliad and could recite the whole thing (in Greek? English? dunno that either) except for the catalog of ships, but he said he could relearn that at any time. That’s strictly an historically useful bit of the text, but doesn’t have much mnemonic formula.
Sidebar — One scholar of Homer teased that the poet’s use of “rosy-fingered dawn” could, due to the contextual nature of ancient Greek, be just as easily translated as “pink-toed dawn”. :^)
That it does indeed AND you can buy paints that are magenta, so you don’t have to mix that color. I have a set that DOES contain a magenta; but besides swatching it, I’ve NEVER used that color.
There are, as you no doubt know, many proposed mechanisms to translate between pigment colors and RGB monitor signals (e.g. Pantone). Artists who work on computers for websites have faced this problem for a few decades, and it's still not a solved problem -- there are only approximations.
Take an apple. Paint a picture of it. Take a photo of the painting. Display it on a monitor. Print it out on a high-quality color laser printer. They'll all be subtly different.
For millennia, humans experienced almost all colors as reflected light -- a sunlit garden, an apple tree, the face of a lover -- and our brains got very good at discerning color that way. The only additive light sources were the Sun (and you better not look directly at it), fire, lightning, fireflies, etc. which are all very transient. Even electric light bulbs -- who stares at a lightbulb expecting to see something? We only use it to illuminate reflective objects.
The introduction of TV displays and computer monitors changed that, and transmitted light sources are now common everywhere. Artists are still tearing their hair out trying to get a computer image to look exactly like their pigment-based creation.
As one trained in physics, but having many family and friends who are artists, I have watched this evolution for the past decades with great interest.
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