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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.

>I'm sure you could find myriad examples of this in the natural world.

Can you think of any?

yaky (https://news.ycombinator.com/item?id=43584334) gave a great example of hummingbirds liking purple.

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.

The purple you saw in those onions is literally a neurological glitch. Your brain inventing a color that doesn’t exist in the spectrum. When red (long) and blue (short) wavelengths hit without green (mid), your visual cortex makes up purple as a placeholder. Your avoidance wasn’t caused by the color itself (a mental construct), but by the brain using this imaginary hue as a proxy for past onion trauma.

This mirrors how we treat UI error messages. A "404" doesn’t cause missing data, it’s just the system’s way of flagging underlying issues. The real causal chain was anthocyanins → wavelength reflection → neural pattern-matching → memory recall. Purple was the middleware, not the root process.

Fun twist. Those fried onions’ brown does have causal ties to flavor. Maillard reaction products directly interact with taste receptors. The universe trolls us with color semantics, but chemistry always wins.

It might not exist in the spectrum, does that mean it doesn't exist? You're arguing and conflating two different things here. On the one hand, you're implicitly arguing that a colour can't exist unless it corresponds to a singular frequency of light, which I've already argued against. This is no more meaningful than arguing that tables and chairs are mental constructs because it's all quarks and electrons at the end of the day. Emergent properties exist and can have causal effects, most philosophers and scientists are in agreement about this.

The other is that a qualia or the mental experience of seeing purple is the same thing as perceiving purple as distinct from other colours in a physical object. I'm not talking about the qualia. In fact, I hate the concept of qualia, because whenever it's introduced into philosophical discussions, the discussion devolves into epicycles of meaningsless discussion of definitions and nomenclature and ends up going nowhere.

No, the purple was there. You say all that was there was some chemicals that only reflects certain wavelengths. I say this is what defines the emergent physical property we call the colour purple. You say electrons and quarks, I say tables and chairs. Both are accurate, and certainly not in conflict.

You might say, so how is this distinct from qualia? Well, for the qualia of seeing purple, there is no way even in principle to decide whether my qualia is the same as your qualia. But I can still look at a red onion and tell you it's purple, and you likely would agree unless you're colour blind. So this property of purple is, unlike a qualia, objective, not subjective.

Your critique reveals a crucial conflation between structural emergence and perceptual categorization, a distinction that clarifies why "purple" (as a color category) lacks the causal efficacy you ascribe to it. If you gift me some of your valuable reading time, let's dissect this.

1. Two Types of Emergence

- Structural emergence (tables/chairs): Arises from physical interactions between components. A table's causal power (holding objects) derives from its atomic structure creating macroscopic rigidity. These properties are observer-independent. A laser would detect the table's structural integrity even with no humans present.

- Perceptual categorization (color): Emerges from evolved neurobiology + cultural reinforcement. The "purple" label applied to red onions is a compression algorithm for "reflects 400-450nm + 600-700nm with minimal 500-600nm". This categorization has no causal power beyond its role as an information tag.

2. The "Objective" Color Fallacy

Your intersubjective agreement about purple stems from:

- Shared cone cell biology: 94% of humans have L/M/S photopsins with peak sensitivities at ~560nm (red), ~530nm (green), ~420nm (blue)

- Cultural conditioning: Modern color lexicons standardized via Pantone systems and CIE charts

Yet this consensus doesn't make purple an emergent physical property.

Consider this.

The Himba tribe uses "zoozu" for dark colors (blue/purple/black) and doesn't distinguish purple as a category

Industrial paint manufacturers recognize 12,000+ color terms, far beyond basic spectral labels

Your "purple" onion would register as #6A1B9A in HEX, 17.3° hue in CIELAB, arbitrary numerical tags, not causal agents

3. Causal Efficacy Lies Elsewhere

The chain you described:

Photons → Retinal Activation → Neural Coding → Avoidance

Contains zero causal nodes requiring "purple" as an explanatory variable. Replace "purple" with "wavelength combo X" and the physics/neurology remains identical. Contrast with a table's causal power. Replace "table" with "carbon lattice configuration Y" and you lose the explanatory utility.

4. The Qualia Dodge

You're right to reject qualia-centric debates, but the alternative isn't reifying color categories. Instead, recognize that:

a) The onion's surface selectively reflects wavelengths

b) Your visual system detects this pattern

c) Your brain applies a culturally-learned label

d) The label activates memory associations

The causal oomph lives in the biochemical aversion pathways, not the color label. Change the label (call it "ploobalooba") while keeping wavelength data and aversion remains. Change the wavelengths while keeping the label, and behavior shifts.

5. The Real Emergent Culprit

What does have causal power here is pattern recognition heuristics. Your brain evolved to:

- Create color categories as survival shortcuts ("red" = blood/danger)

- Link these to outcomes via associative learning

These heuristics are genuine emergent properties with causal effects, but they're neural algorithms, not spectral properties. The purple label is their UI, not their codebase.

TL;DR

You're mistaking the map (color categories) for the territory (wavelength interactions). Tables derive causal power from structural emergence, "purple" derives consensus from neuro-cultural emergence. One explains why plates don't fall through surfaces, the other why we argue about onions at barbecues.

>I don't know, but feel free to use a search engine.

I did. I didn't find any. I don't think there are. You made the assertion, so, I thought you might know some.

>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?

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

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

Same with pink.

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.

Color is a mixture of wavelengths of visible light. Mixtures of wavelengths of visible light exist in the wild.

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.

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.

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.

You're confusing the qualia of colour("what it's like" to perceive colour) with the property of colour. Both can be referred to by the word "colour".

You're essentially just arguing that one definition of a noun is "more valid" than another, which is completely arbitrary.

And of course the qualia of colour is entirely subjective and only in the mind. That's literally the definition of qualia. That doesn't mean the property of colour is also subjective, just because it's referred to by the same noun. And besides, qualia is a philosophically controversial term in the first place.

If you were trying to cross a river and someone told you walk over that bridge over there, you wouldn't respond that it's impossible because a bridge is a device that links two computer networks together at the link layer, and couldn't possibly be used a cross a river, would you?

you're right, I'm just arguing that when we talk about colors we talk about the subjective perception of it, the thing that we see, which is what is usually referred to as color in any normal conversation. I didn't know there was a different definition of color which was a synonym of wavelength, in that case you're right. So as you say, the debate is arbitrary because it's about different definitions of color.

However, both measurements of wavelengths, the qualia or subjective one and the numerical wavelength or objective one, both exist only in our minds. There exists a measurement if and only if there exists someone that measures, even if it is an objective measure

Purple is a measurement, but wavelength is a measurement too. Ultimately everything is a measurement to us as that is the only way we can experience "the wild".

But wavelengths are a property of the waves that exist in the wild, while color is a property of our brains interpreting those wavelengths. There's a fundamental difference there: one could say that wavelengths exist independently of the existence of conscious beings (even if no one measures them), while colors only exist if a conscious being can capture photons and has a certain brain system that can interpret those photon's wavelengths.

Wavelength measures something in the wild. Whatever that something is, colour (and thus purple) offers a different way to measure the same thing. While the measuring unit differs, the fundamentals are the same.

interesting, so you're saying wavelengths are also a construct of the human mind (handed with a device to measure them). Maybe then the Buddha was right when he said "form is emptiness"? Which would mean there's no way that something really is independent of the way of looking at it, that things are empty, there are only ways of looking...

There's a common abuse of language that the ancestor comment uses, where we also use the names of colors for the wavelength of the pure light that we perceive them as; perhaps they could have been more specific about that. Hence because of this abuse of terminology we have words like infrared and ultraviolet to refer to spectra beyond human color perception, but are so called for their relation to the particular pure wavelengths that we perceive as red and violet.

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.

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.

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

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.

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.

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.

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

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.

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.