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I love the headline, but unfortunately both the headline and the explanation are wrong. Better explanation: The red, green and blue receptors in the eyes all

I love the headline, but unfortunately both the headline and the explanation are wrong. Better explanation: The red, green and blue receptors in the eyes all respond to all wavelengths of light, they're just more sensitive at red, green and blue respectively. When violet hits those receptors, it doesn't hit any of the receptors at their peak sensitivity point. All three receptors fire. However, the green receptor has much better sensitivity than the red receptor, so violet triggers the strongest response in blue and red. If the red receptor was more sensitive, we'd probably interpret violet as a shade of blueish-brown rather than of purple. The headline: Purple definitely exists. The eye & brain interpret purple and violet the same, but in the physical world they are different colors, and they both exist in the wild. Purple is a mixture of red & blue, violet is the highest visible frequency. A purple flower is a flower that absorbs green and reflects red & blue. A violet flower is a flower that absorbs red, green and blue and reflects violet.

AlotOfReading 2y ago
Colors like purple are called "extraspectral" to distinguish them from the spectral colors like violet.
- Anon84 2y ago
  Same with pink.
bryanlarsen 2y ago
P.S. Tetrachromats can distinguish between violet and purple, unlike us normal humans.
- stvltvs 2y ago
  Not true. Human tetrachromats have an extra kind of receptor somewhere between the blue and red receptors' sensitivity. This doesn't help with colors like violet that are outside of that range. Also, purple (a non-spectral color) is easily distinguished from violet (a spectral color) if you see them side-by-side.
  - bryanlarsen 2y ago
    There exists a shade of purple that is indistinguishable from violet because it triggers the cones of the eyes at the same level that violet does. You can buy paint called "violet". This isn't the spectral violet, it's a shade of purple that looks very similar to spectral violet. Tetrochromats can distinguish between that purple shade and real violet. But if you mixed the paint using 4 tints rather than 3 you could fool them too.
    - stvltvs 2y ago
      Source? edit: You may be confusing tetrachromacy with people who don't have a lens and can therefore perceive ultraviolet light that's normally filtered out. These folks can see shades of violet where other people don't because the blue receptors are being stimulated by the ultraviolet light.
mtlmtlmtlmtl 2y ago
Agreed. It's simply philosophically sloppy to suggest that purple, brown, and really any other colour don't exist without qualifying what one means by existing in this context, and why that definition of the word is used. In this case, it seems the "what" is that for a colour to "exist", it has to be a distinct, isolated frequency of light, and (for some reason) it needs to appear in a logical place in the frequency space in relation to other colours. They don't answer the "why" question, and I think if they tried, they would find it difficult, because it's completely arbitrary and in conflict with reality. Just because some colours do in fact correspond to frequencies of light, that doesn't mean all colours have to. There's a reason we have the terms primary and secondary colour. Some colours are emergent from mixing other colours together. Does that mean they can't appear in the natural world, being discriminated by sensory systems? No. Does purple cause things to happen? I'm sure you could find myriad examples of this in the natural world. Ironically, the only thing here that only exists in our brains, is the notion that purple doesn't exist.
- VectorLock 2y ago
  >I'm sure you could find myriad examples of this in the natural world. Can you think of any?
  - bryanlarsen 2y ago
    yaky (https://news.ycombinator.com/item?id=43584334 https://news.ycombinator.com/item?id=43584334) gave a great example of hummingbirds liking purple.
  - mtlmtlmtlmtl 2y ago
    Even better, I can tell you one I experienced literally today. I was at a barbeque, and the people hosting put out one bowl of diced red onion, which despite the name was purple, as it tends to be, and a bowl of crispy fried onion, which was brown. I reached for the fried onion, and avoided the red(purple) onion, because I always hated red onion. Now, if you want to be annoying, you could make all sorts of red(heh) herring arguments about the cause of me avoiding the red onions being their flavour and aroma in the past having caused me not to like onions, and that's all true. But effects can have multiple causes, and it's also true that the distribution of pigments in the onion leading to an emergent property we dub "purple" did in fact convey information to me that caused me to decide not to eat them. I didn't smell them or taste them. Information was transmitted from onion to mind, via the electromagnetic field. Clearly the emergent property of purple colour has a causal effect here. As for other examples in the natural world of non-human plants an animals, I don't know, but feel free to use a search engine. But since the colour purple is found in all sorts of life forms(including humans, and all sorts of life forms(including) are able to perceive and discriminate it from other colours, it's fair to assume that the colour purple is out there having all sorts of causal effects.
happytoexplain 2y ago
>All three receptors fire. However, the green receptor has much better sensitivity than the red receptor, so violet triggers the strongest response in blue and red. I'm confused - it sounds like you're saying it's so off-peak for all of them that, even though it's more proximal to blue, it is effectively equally out-of-range for all three - except that the green receptor is more sensitive. But then that would mean it should look more green, rather than more red and blue, no?
- bryanlarsen 2y ago
  More sensitive is a relative term rather than an absolute term -- the green cone selects for its color better than the red cones do.
broof 2y ago
Violet in the rainbow is not a purple hue, it is a deep blue. Illustrations often color it more purplish but that is inaccurate
- bryanlarsen 2y ago
  You usually can't see the really purple-y violet in a rainbow because it's quite dark -- it's easily absorbed by the atmosphere and our color cones aren't very sensitive to that wavelength. But it's there if you amplify it.
- stvltvs 2y ago
  Exactly this, purple ≠ violet. They don't even look the same. You won't see violet on a computer screen because it's a higher frequency than what blue LEDs produce. You won't see it on the output of consumer-grade printers for similar reasons regarding the color of the ink. The easiest way to see actual true violet is to pass sunlight through a prism onto a white surface. Purple on the other hand is a mixture of red and blue frequencies that stimulate both kinds of receptors in your eyes. It looks like a reddish blue that can't be produced by any one frequency of light. True violet looks like a deep, deep blue without any red tint.
mfeole 2y ago
I think you're misinterpreting color and wavelength. No color exists "in the wild". Colors only exist in the consciousness of beings that can capture photons. Wavelengths do exist in the wild I guess, or at least it's a human description of how electromagnetic waves move in the wild.
- bryanlarsen 2y ago
  Color is a mixture of wavelengths of visible light. Mixtures of wavelengths of visible light exist in the wild.
  - pixl97 2y ago
    Color, as we know them, are a human interpretation of wavelengths and one we know is semi-subjective based on things like color blindness. A creature with less sensitive receptors could see one color were we'd see a much wider range. The reverse is also true that a creature with more sensitive receptors could see far more colors than we do.
  - mfeole 2y ago
    No, color is a subjective experience a conscious being has. Different colors each correspond to different mixtures of wavelengths, but that doesn't mean they are the same thing. Color is the thing that you see with your consciousness. The difference is fundamental: wavelengths exist independently of the existence of conscious beings, while colors only exist if a conscious being can capture photons and has a certain brain system that can interpret those photon's wavelengths.
    - AlotOfReading 2y ago
      Colors don't even require photons. There's a phenomenon called phosphenes that produces colorful lights (green and purple for me). You can see them by rubbing your eyes sufficiently hard, or copy Newton and stick a blunt needle in your eye. They're caused by mechanical deformation in your optical cells rather than any photons being captured, but they produce the experience of color regardless.
erehweb 2y ago
I think you are misunderstanding the purpose of a headline. "Purple exists only in our brains" is a reasonable summary. Your last paragraph is not a headline.
- bryanlarsen 2y ago
  It's a reasonable summary of a portion of the article. I assert that the portion it summarizes is wrong, making the headline also wrong.

AlotOfReading 2y ago

Colors like purple are called "extraspectral" to distinguish them from the spectral colors like violet.

Anon84 2y ago
Same with pink.

bryanlarsen 2y ago

P.S. Tetrachromats can distinguish between violet and purple, unlike us normal humans.

stvltvs 2y ago
Not true. Human tetrachromats have an extra kind of receptor somewhere between the blue and red receptors' sensitivity. This doesn't help with colors like violet that are outside of that range. Also, purple (a non-spectral color) is easily distinguished from violet (a spectral color) if you see them side-by-side.
- bryanlarsen 2y ago
  There exists a shade of purple that is indistinguishable from violet because it triggers the cones of the eyes at the same level that violet does. You can buy paint called "violet". This isn't the spectral violet, it's a shade of purple that looks very similar to spectral violet. Tetrochromats can distinguish between that purple shade and real violet. But if you mixed the paint using 4 tints rather than 3 you could fool them too.
  - stvltvs 2y ago
    Source? edit: You may be confusing tetrachromacy with people who don't have a lens and can therefore perceive ultraviolet light that's normally filtered out. These folks can see shades of violet where other people don't because the blue receptors are being stimulated by the ultraviolet light.

mtlmtlmtlmtl 2y ago

Agreed. It's simply philosophically sloppy to suggest that purple, brown, and really any other colour don't exist without qualifying what one means by existing in this context, and why that definition of the word is used. In this case, it seems the "what" is that for a colour to "exist", it has to be a distinct, isolated frequency of light, and (for some reason) it needs to appear in a logical place in the frequency space in relation to other colours. They don't answer the "why" question, and I think if they tried, they would find it difficult, because it's completely arbitrary and in conflict with reality. Just because some colours do in fact correspond to frequencies of light, that doesn't mean all colours have to. There's a reason we have the terms primary and secondary colour. Some colours are emergent from mixing other colours together. Does that mean they can't appear in the natural world, being discriminated by sensory systems? No. Does purple cause things to happen? I'm sure you could find myriad examples of this in the natural world. Ironically, the only thing here that only exists in our brains, is the notion that purple doesn't exist.

VectorLock 2y ago
>I'm sure you could find myriad examples of this in the natural world. Can you think of any?
- bryanlarsen 2y ago
  yaky (https://news.ycombinator.com/item?id=43584334 https://news.ycombinator.com/item?id=43584334) gave a great example of hummingbirds liking purple.
- mtlmtlmtlmtl 2y ago
  Even better, I can tell you one I experienced literally today. I was at a barbeque, and the people hosting put out one bowl of diced red onion, which despite the name was purple, as it tends to be, and a bowl of crispy fried onion, which was brown. I reached for the fried onion, and avoided the red(purple) onion, because I always hated red onion. Now, if you want to be annoying, you could make all sorts of red(heh) herring arguments about the cause of me avoiding the red onions being their flavour and aroma in the past having caused me not to like onions, and that's all true. But effects can have multiple causes, and it's also true that the distribution of pigments in the onion leading to an emergent property we dub "purple" did in fact convey information to me that caused me to decide not to eat them. I didn't smell them or taste them. Information was transmitted from onion to mind, via the electromagnetic field. Clearly the emergent property of purple colour has a causal effect here. As for other examples in the natural world of non-human plants an animals, I don't know, but feel free to use a search engine. But since the colour purple is found in all sorts of life forms(including humans, and all sorts of life forms(including) are able to perceive and discriminate it from other colours, it's fair to assume that the colour purple is out there having all sorts of causal effects.

happytoexplain 2y ago

>All three receptors fire. However, the green receptor has much better sensitivity than the red receptor, so violet triggers the strongest response in blue and red. I'm confused - it sounds like you're saying it's so off-peak for all of them that, even though it's more proximal to blue, it is effectively equally out-of-range for all three - except that the green receptor is more sensitive. But then that would mean it should look more green, rather than more red and blue, no?

bryanlarsen 2y ago
More sensitive is a relative term rather than an absolute term -- the green cone selects for its color better than the red cones do.

broof 2y ago

Violet in the rainbow is not a purple hue, it is a deep blue. Illustrations often color it more purplish but that is inaccurate

bryanlarsen 2y ago
You usually can't see the really purple-y violet in a rainbow because it's quite dark -- it's easily absorbed by the atmosphere and our color cones aren't very sensitive to that wavelength. But it's there if you amplify it.
stvltvs 2y ago
Exactly this, purple ≠ violet. They don't even look the same. You won't see violet on a computer screen because it's a higher frequency than what blue LEDs produce. You won't see it on the output of consumer-grade printers for similar reasons regarding the color of the ink. The easiest way to see actual true violet is to pass sunlight through a prism onto a white surface. Purple on the other hand is a mixture of red and blue frequencies that stimulate both kinds of receptors in your eyes. It looks like a reddish blue that can't be produced by any one frequency of light. True violet looks like a deep, deep blue without any red tint.

mfeole 2y ago

I think you're misinterpreting color and wavelength. No color exists "in the wild". Colors only exist in the consciousness of beings that can capture photons. Wavelengths do exist in the wild I guess, or at least it's a human description of how electromagnetic waves move in the wild.

bryanlarsen 2y ago
Color is a mixture of wavelengths of visible light. Mixtures of wavelengths of visible light exist in the wild.
- pixl97 2y ago
  Color, as we know them, are a human interpretation of wavelengths and one we know is semi-subjective based on things like color blindness. A creature with less sensitive receptors could see one color were we'd see a much wider range. The reverse is also true that a creature with more sensitive receptors could see far more colors than we do.
- mfeole 2y ago
  No, color is a subjective experience a conscious being has. Different colors each correspond to different mixtures of wavelengths, but that doesn't mean they are the same thing. Color is the thing that you see with your consciousness. The difference is fundamental: wavelengths exist independently of the existence of conscious beings, while colors only exist if a conscious being can capture photons and has a certain brain system that can interpret those photon's wavelengths.
  - AlotOfReading 2y ago
    Colors don't even require photons. There's a phenomenon called phosphenes that produces colorful lights (green and purple for me). You can see them by rubbing your eyes sufficiently hard, or copy Newton and stick a blunt needle in your eye. They're caused by mechanical deformation in your optical cells rather than any photons being captured, but they produce the experience of color regardless.

erehweb 2y ago

I think you are misunderstanding the purpose of a headline. "Purple exists only in our brains" is a reasonable summary. Your last paragraph is not a headline.

bryanlarsen 2y ago
It's a reasonable summary of a portion of the article. I assert that the portion it summarizes is wrong, making the headline also wrong.