Well this WU primarily exists because I have a question, and I would like someone around in Biology or Medicine to answer it.

It is an empirical fact that the human eye is sensitive to different wavelengths in the electromagnetic spectrum, and this is the origin of colours. Other physiological effects of colour are also empirically verified. For example, when we mix Red, Green and Blue light we see White light, and this is something that is true for everyone.

However, what about the actual sensation of colour. Has anyone devised an experiment which would be able to determine whether the actual senstion is the same for different people or not? For, after all, what you see as yellow I could see as red, and what you see as red I could see as yellow. We would of course never know for we would agree on names and other physiological effects like what happens when we mix colours(Hope I'm making myself clear). But it might be possible(probably by means such as giving direct signals to the brain) to actually determine the sensation of colour. Has anything of this sort been done?

As both dmd and rp began to answer this then balked at it (then came back and had another go... they're gone again now), I am chary of attempting it myself; but perhaps unlike them, I don't feel I need any detailed knowledge of rods and cones, of how the optic nerves and the visual cortex work. (Gilbert Ryle said this better, but I can't find the quote.)

This node contains two topics. (i) whether colours are real; (ii) whether people's actual sensations of colours are different. I'll answer them separately.

What on earth does it mean to say colour (or a colour) "exists"? Or "doesn't exist?" What on earth are you trying to say about it? Unicorns don't exist—if you search the world you won't find any. The lost poems of Gallus don't exist—they used to but the manuscripts have been destroyed by the ravages of time. Phlogiston doesn't exist—it was a hypothetical substance, in a theory no longer held. Here are three good examples where we say X doesn't exist—and 'exist' in each case has a different sense. Unicorns don't exist and dodos don't either, but in different ways.

How can you apply this to colours? In science fiction, you might describe an alien race as seeing in a different part of the spectrum—but no, those wavelengths exist too, even if we can't see them. You wouldn't say the bee-colours the fiction-writer describes "don't really exist". What doesn't exist is the giant robot bee that can see them.

A colour intermediate between red and green perhaps? Other than yellow...? A colour that's simultaneously red and green all over? That can't exist. That's what set Wittgenstein back onto philosophy. But here we're screwing up our minds trying to imagine queer non-standard colours so that we can say they don't exist, i.e. that you couldn't ever really see such a colour.

Unlike the ones you can see: red, green, blue, white, fawn, ... It simply makes no sense whatsoever to look at something you can see and say "I can't see that". If it's blue, and you're not colour-blind, and you've got enough daylight, and your head isn't in a photographer's black hood (etc.), you can see it. It's there. It's blue.

But "blue exists"? "blue doesn't exist"? Both nonsense. "Exist" isn't something you say about colours.

The second question is of the existence of qualia (Latin plural of quale "what sort of?"). Some philosophers believe that as well as everything that goes on in the brain—all the photons hitting rhodopsin in the retina, the firings of the optic nerves, the activation of different regions of cortex to process the incoming message "something blue out there"—in addition to all this, they think, there is something extra: qualia: "what blue looks like"? "How it feels to see blue"?

So, according to them, a brain could undergo all the pings and bloops that indicate "blue" but somewhere deep inside a little detached Cartesian spirit within the brain, some undetectable something lights up as "yellow".


We concede that this curiously-wired-up person reacts to colours in "normal" ways (soothed by green, hot and bothered by red, uses the same noise red to point at the same flowers, fire-engines, blood, and so on that the rest of us do). Note that colour-blind persons don't count: they behave palpably differently (e.g. on tests). So what is there left? If their pulse goes up in a bright red room, and mine does too, if their threshold of perception is the same (say it's easier to detect a very faint red than a very faint yellow)... concede all the physiological inwardness, all the brain states, and there's nothing left. (Technically this line I'm rubbishing is called the inverse spectrum argument.)

Of course, if they see it differently and we can detect a different brain state by external means (ECG or fMRI) then we're just in the realm of experimental physiology. There could well be such non-standard wirings. But they don't involve qualia. There are no such things as qualia.

What on earth could it mean to say someone "saw" something differently when everything detectable is the same? What would you be trying to say about them? Nothing.

To help settle this, I'll define color in such a way as to divorce it from perception by eyes:

color n. A property of electromagnetic radiation such that one band of wavelengths is more intense than an adjacent band.

© Yerrick 2001.

Red objects are perceived as red because the cones of our eyes respond to wavelengths around 700 nm differently from 580 nm (yellow), 520 nm (green), or 470 nm (blue). ariels claimed that the color magenta was a counter-example, but it merely consists of power peaks in both the visible blue and visible red bands.

This definition of "color" also generalizes to radio transmission and receiving (radio stations come in on different "colors") and reminds a fellow of how fiber optics works. Salon.com has published an article (http://www.salon.com/tech/feature/2003/03/12/spectrum/index.html?x) about how this conception of spectrum as color could make the FCC's job less important.

Colour does exist. 'Plasmic light-rays', 'photons', and 'radiation' may or may not exist, and they may or may not cause my seeing colour. But colour does exist with or without them.

Colour refers to qualia*. I know that there is red, blue and even green. I can see them in my head. I am more certain that there are these colours than I am sure of the existence of this computer (Think Descartes' Demon, or if you must, The Matrix). I might not be sitting at a table typing on a keyboard. There may be nothing 'white' in front of me. But there most certainly is some white here. I can see it. I might be imagining that it's 18 inches in front of my face, but I don't see how I could be imagining that I have an experience of white.

And colour does indeed refer to your experiences. You can have a colour in your imagination, while at the same time having no 'electromagnetic radiation' of the type to stimulate your 'rods and cones' shuffling around in there.

We assume that, while they have different causes, the colours in our heads and in the outer world are the same. We could be wrong. Maybe they are completely different things. If the title of this node means only that Outside-of-your-head-colour doesn't exist, I will not argue. But by the good solid definition of colour as qualia, colour exists.

* Which is not to say that it doesn't refer to something else too, but it does indeed refer to qualia, and qualia surely exist.

Does color exist?

Well, like many a philosophical question, I think it comes down to what you mean by exist and what you mean by color. I think people generally have 3 things in mind when they speak of color:

  1. The human perception of color
  2. The property of electromagnetic radiation
  3. The subjective sensation of color

So let me define clearly what I mean by each of those, and then talk about in what sense they exist.

In the first sense, I refer to the fact that there is a property of things that humans perceive that we call color. I assert that I can prove that this exists pretty easily, because, hey, traffic lights work. What I mean is that I can prove the existence of color as a property that (most) humans can perceive as much as I can prove the existence of any other property (like size, shape, texture), because I can tell by observing people react to this property and use it in cases like the traffic light to coordinate their behavior. So, the hypothesis that a property called color exists which relates to the perceptions of different people is pretty well supported. The point here is that even someone who is color blind, or even completely blind can still surmise in this way that colors exist. So far, we've said that some property called color exists and that there is a correspondence between how many people sense it, though this does not say their sensations are the same.

The second sense in which people use color is with respect to light. We refer to light as having a color, corresponding to the mixture of wavelengths present in that electromagnetic radiation. There are both spectral colors, which correspond to light with only one narrow range of wavelengths (e.g. red, green, blue), and then there are other colors that are mixtures of several wavelengths in certain proportions (e.g. cyan and magenta). This second property, the spectrum of the light, can again be verified with a spectrometer without the faculty of human color perception. This, of course, is something humans discovered much later than the first sense, but the reason we call this color is that we can observe a correlation between the properties of electromagnetic waves leaving an object and the color that people say they perceive. Simply put, if we replace a the red light in a traffic signal with another source of light with the same spectral characteristics (something with a strong peak in the 600-700 nm range or so), people will react in approximately the same way. In so far as this is true, we can ascribe the spectral properties of light coming from an object as the cause of the perception of color by humans, without really having to know anything about HOW humans process the light, so long as it seems plausible that they could.

So, it seems that in the first two senses, color exists, in so far as it can be empirically verified through observation. Objects emit light, and that light induces a particular perception in most humans. Generally, though, when people ask about color in a philosophical context, though, they mean the third sense.

By the subjective sensation of color, I mean the sense of what red or blue "looks like" when a person with color sensitive vision looks at an object. This, I suppose, is what is meant by qualia. Certainly it's clear that people believe they have such a sensation, again because this is the best explanation of the fact that they claim having such a sensation and it correlates in a single individual with the other senses in which we use the term color (ie. someone will report that something looks red when we show them an object with the right light spectrum that other people also say is red). Generally the question is then whether the subjective sense of red is the same for all individuals, whether red looks the same to me as it does to you.

When we've narrowed the question down this far it clearly becomes hard to answer. If we are willing to make the materialist hypothesis that there is a one to one relationship between the physical state of the body and brain and the subjective perceptions of a person's mind, then this question is answerable through scientific testing. I'm fairly certain that at the moment we don't really know enough about the brain to give a definitive answer, but in the future it's likely we will be able to. If, however, you are not willing to make the materialist hypothesis, then without some further assumptions there is no way of knowing whether colors are perceived the same way in every person in the empirical, scientific sense. With other metaphysical assumptions, you might be able to make some conclusion, but otherwise you're stuck.

Personally, I don't subscribe to any other metaphysical definition of existence. I would say I know that I get a certain sensation when I see a color. I cannot doubt that because it is simply there in my mind, undeniably, as much as any other of my sensations or ideas. As to how color exists in the minds of others, I know that there is this correspondence between my sensation of colors and others' apparent perception of colors (as they report it, and as reflected through their actions). It is that correspondence that exists, and that's what I really mean when I say that color exists. To me, any further, untestable sort of existence is nonsense.

So, if you're reading this and you just think it's pointless, useless, or redundant drivel, then let me know. I may consider removing it.

I think the basic point of the original write up in this node has been missed slightly.

Suvrat (I believe) was just simply asking the visual equivalent of "If a tree falls in a forest, and nobody's around, does it make a sound?" In other words, would color exist if there were no eyes around to perceive the light and its many wavelengths?

Being a fine artist and one-time painter I know quite a bit about color theory and what colors to mix with what to get what. As such, I have often in my mind wondered, usually while in art classes, "What if this red I'm seeing actually looks like what I perceive as yellow to that person over there? Is this impossible to know?" But only in my mind, because I was afraid of sounding crazy. I was relieved to see this node and that others have had the same thoughts.

I have always wanted to somehow see what it was like to see the world through another person's eyes just for a moment. Maybe nothing would look different. Maybe everything would. It's one of those things that will eventually drive you crazy if you think about it long enough.

Like the tree falling in the forest thing.
