When I was a kid, I used to wonder if everyone saw the world in the same way. We can all look at the same grass, but maybe the color I called green showed up in my brain as the color my friend called blue. Maybe all of our colors were shifted around to the point where all the colors were accounted for, but how we perceived them was shuffled up. I thought it would be remarkably exciting, and hoped that I could see the world through someone else’s brain to see if, in fact, this was true.


My eight year old self would be bitterly disappointed technology today has not progressed far enough to make that wish a reality. At the time, we had to settle the debate by another manner – asking an adult, a source of concrete and immutable knowledge. The answer I was given was that everyone sees the same colors of course (although why this was so obvious was never really clear) and if they didn’t it wouldn’t matter much since we couldn’t tell. Color was “real” – bits of light had a color (later I found out we could call it the wavelength of a photon), it hit our eyes, and our brains converted it to a beautiful image.

The only problem is that this is wrong.

Color as Wavelength

Well, alright. Before you get upset, it isn’t completely wrong. We were all taught about Sir Isaac Newton who discovered that a glass prism can split white light apart into its constituent colors.


While we consider this rather trivial today, at the time you’d be laughed out of the room if you suggested this somehow illustrated a fundamental property of light and color. The popular theory of the day was that color was a mixture of light and dark, and that prisms simply colored light. Color went from bright red (white light with the smallest amount of “dark” added) to dark blue (white light with the most amount of “dark” added before it turned black).

Newton showed this to be incorrect. We now know that light is made up of tiny particles called photons, and these photons have something called “wavelength” that seems to correspond to color. Visible light is made up of a spectrum, a huge number of photons each with a different wavelength our eyes can see. When combined, we see it as white light.


So this appears to resolve my childhood debate. Light of a single wavelength (like that produced by a laser) corresponds to a single “real” color. The brain just translates wavelengths into colors somehow, and that is that. There’s just one problem.

We’re missing a color!

Color as Experience

To find out just what we’re missing, we have to consider how we can combine colors. For instance, you learned some basic color mixing rules as a kid. In this case, let’s use additive color mixing since we’re mixing light.


Let’s find two colors on the spectrum line, and then we can estimate the final color they’ll produce when you mix them by finding the midpoint.

Red and green make yellow.


Green and blue make turquoise.


Red and blue make…


Green? What? That doesn’t seem to make any sense! Red and violet make pink! But where is pink in our spectrum? It’s not violet, it’s not red – it seems like it should be simultaneously above and below our spectrum. But it’s not on the spectrum at all!

So we’re forced to realize a very interesting conclusion. The wavelength of a photon certainly reflects a color – but we cannot produce every color the human eye sees by a single photon of a specific wavelength. There is no such thing as a pink laser – two lasers must be mixed to produce that color. There are “real” colors (we call them pure spectral or monochromatic colors) and “unreal” colors that only exist in the brain.

A Color Map

So what are the rules for creating these “unreal” colors from the very real photons that hit your eye? Well, in the 1920s W. David Wright and John Guild both conducted experiments designed to map how the brain mixed monochomatic light into the millions of colors we experience everyday. They set up a split screen – on one side, they projected a “test” color. On the other side, the subject could mix together three primary colors produced by projectors to match the test color. After a lot of test subjects and a lot of test colors, eventually the CIE 1931 color space was produced.


I consider this to be a map of the abstractions of the human brain. On the curved border we can see numbers, which correspond to the wavelengths in the spectrum we saw earlier. We can imagine the spectrum bent around the outside of this map – representing “real” colors. The inside represents all the colors our brain produces by mixing – the “unreal” colors.

So let’s try this again – with a map of the brain instead of a map of photon wavelengths. Red and green make yellow.


Green and blue make turquoise.


Blue and red make…


Pink! Finally! Note that pink is not on the curved line representing monochromatic colors. It is purely a construction of your brain – not reflective of the wavelength of any one photon.

Is Color Real?

So is color real? Well, photons with specific wavelengths seem to correspond to specific colors. But the interior of the CIE 1931 color space is a representation of the a most ridiculously abstract concept, labels that aren’t even labels, something our brain experiences and calculates from averaged photon wavelengths. It is an example of what philosophers call qualia – a subjective quality of consciousness.

I later learned that my childhood argument was a version of the inverted spectrum argument first proposed by John Locke, and that the “adult” perspective of everyone seeing the same colors (and it not really mattering if they didn’t) was argued by the philosopher Daniel Dennett.

I have come no closer to resolving my question from long ago of “individual spectrums” – but for the future, I vow to pay more attention to the idle questions of children.

127 thoughts on “Color and Reality

  1. Mathematically, the physical light spectrum is group R, while our vision and perception of the same is group Z. These correspond to the difference between real numbers (R) and integer numbers (Z).

    Something to think about when you wonder if you “see” reality.

  2. One important distinction is that, other than in cases of actual frequency-insensitivity, people can actually agree on ‘what is red’ or ‘what is blue’, when they perceive it. (whether some people know ‘what is mauve’ vs others is addressed in the comments above — for the sake of argument, let’s assume basic correspondence between rod/cone/neural dispositions).

    The real question is whether blue ‘seems like’ blue, regardless of whether it can be identified as ‘blue’. Hence ‘favorite colors’. Some colors just feel more comfortable.

    I’d actually be interested in discovering whether or not human ‘outliers’ that (possibly) detect UV or IF frequencies report different impressions of the colors of a standard spectrograph. (actually, I think color space is more like a volume rather than a 2d plot)


  3. I’m not sure your childhood question is well posed. What does it mean, in an absolute sense, to “perceive” colours in different ways? We all have relative interpretations of colours… green like grass (or more abstractly, environmentalism), blue like the sky. But these associations are relative – we see two things which are similar in colour, and link them. But I don’t think there is any reason to believe there is such a thing as ‘absolute’ meaning of a particular colour, something which your question presupposes.

    We could come up with questions which are closer to being well-posed:
    => Are there any innate associations between concepts and colours, or are these associations purely learned? Test: somehow switch around colours coming into some animals’ eyes as technology allows for this, and test for behavioural differences. Eyes are worse at perceiving particular colours (e.g. blue, as is well known, and probably related to the chart you posted).
    => Do neural pathways in the same relative spatial position in the brain get triggered by light of particular colours, or is the configuration of the brain with respect to colour perception different from human to human?

  4. Well, since developmental neuroscience has shown that the brain’s coding of sensory information is partially dependent on the environment it experiences for about the first 6 months of life as well as on genetics, then I think its fair to say that the way color is represented physically in the brains of two given people could vary significantly. Additionally, I can imagine a case where one person could perceive two different light sources as being the same color, while another person saw them as slightly different colors. This is due to the fact that there are nearly infinite combinations of wavelength and intensity for each perceivable color, and what combinations map to what colors is dependent on the characteristics of a person’s photoreceptor cells, which can vary with genetics. However, I disagree with your assertion that color is a highly abstract thing in the brain. Every perceivable hue corresponds directly to a certain set of activation intensities for the three types of cone receptors. Every color you can think of becomes “real” (having a direct, unique physical representation) before it leaves your retina.

  5. I also questioned this when I was a kid, and later when i grew up, this is my non-scientific explanation that we all really do see the same colors :

    Colors have much more meaning than just energy levels or RGB values. Before we were even born, we already have pre-defined notions of what colors mean. Through millions of years of evolution, we “know” innately that meat is red ( so it makes us hungry, or aggressive) , and grass is green ( which makes us relaxed and soothing) , and so on. Of course that is a generalization, but the idea is that our “color processing unit” must be producing the same signal to distribute to other parts of the brain, that handle mood, hunger, emotions, etc. If we were all “seeing” different colors, the other units would have to somehow re-calibrate against some sort of reference color scheme when we were born. But obviously, as a baby, we can already associate colors with emotional responses.

  6. I actually thought the same thing when i was kid, and you didnt prove if its wrong or not.
    One more thing – I thought that, if the theory that everyone sees colors different were true, then that would explain why my favourite color is green(like grass), but my friends blue (like sky), when actually he would see the sky green, and all the people would have the same favourite color actually, just we would know them by different names, and different objects.
    Hope you understood what i meant 😀

  7. I always had the same question in my mind.. what is blue to me might be a different color altogether for someone else… and so can be said for the combination of colors… and different colors arouse different feelings in people can that be a proof that they are seeing something different.. how can one prove???

  8. Here’s an interesting question: why color? It’s clear that many people have had your same childhood question. But in principle it could be applied to smells, sounds, textures, or shapes as well. Yet we all fixed on color. Clearly there is some common mechanism at work. And I wonder if those of us who had this thought as children all share some particular brain physiology…

  9. I think the confusion about creating pink makes more sense if you realize that the color spectrum circles in on itself. In every situation you have two different ways to find the midpoint. Use the SMALLEST distance and you will find pink. Am I confused on this?

    • Hi Chris – The color spectrum of visible light does not circle in on itself – it’s a tiny slice of the larger electromagnetic spectrum. A color wheel created by artists does circle in on itself. That’s the point – that our brain creates this “loop”. There are no pink photons.

  10. Wow, so when we say “I see colour”, there is a subject “I”, and a verb “see colour”, but no object as such. For colour is an experience of consciousness in the brain when subjected to photons via the eye, as proven by the “colour” pink, which does not exist outside of consciousness/the brain.

  11. I’d just like to point out an interesting correlary. In your example where you use the CIE color space and add greeen and blue to see turquoise, are you really seeing turquoise? Even if you moved your circle over to the line corresponding to roughly that color, around 495, are you seeing turquoise?

    Of course you aren’t. Your monitor can’t display turquoise. Your monitor can display exactly 3 colors: red, green and blue.

    Imagine if you will that your cones can detect one of those three colors (I don’t remember the biological basis, each cone might have multiple receptors, but the concept is the same). Each receptor detects peak amounts of light at red, green, or blue, but tapers off as you go away from that, kind of like a bell curve.

    The important thing though is that these bell curves overlap. So when you see light at 495 it stimulates a bit of your blue and a bit of your green receptor. The monitor simulates that with 520 + 470.

    After all, haven’t you ever wondered why there are 3 primary colors? if it’s a spectrum, you could create any color by combining 2 primary colors? If it’s cyclical why can’t there be 4, 5, or more?

    Maybe, just maybe, the 3 primary colors correspond to 3 different color receptors in your eye.

    To bring this rant back to topic, you’re right, other people may see things differently. After all, we’re talking about nature, which is imprecise. There’s a strong possibility, maybe even a high probability, that their detector bell curves are a slightly different shape or shifted slightly up or down the spectrum, which means what they see *IS* different.

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  13. I think the question of color perception is really an excellent example of what is meant by “perception”. Perception is a stable state of the brain’s neural net; a weighted balance of connected neurons. Any given perception or awareness is never the product of a single neuron firing. One of the simplest examples of this is the retina (Latin “little net”.) Every perceived color is a balance of the discharge of receptor cells “tuned” to be stimulated to different degrees by each wavelength of light. So what we call perception is really just the stable states that are triggered by the photic stimulus. To say that they are the same or different to each viewer implies that they are somehow reconstructed in miniature inside our brains. They’re not.
    BTW calling them “particles” or “waves” is just a way of describing the behavior of photic energy. Neither model is a completely accurate.

  14. I believe the actual perception of colour is generated by the brain. I evidence this by the following..

    I am red green colour blind. This is a bit of a misnomer, for most of the normal tonal range I can distinguish red and green easily. Actually I am a designer and my colour blindness has not proved too much of a hinderance. My brother has the same kind of colour blindness but he has a much harder time of distinguishing colours. I know for a fact I am using other clues to deduce the actual colour of an item. One of the most important things is tone (something CB people can distinguish better than non CB). This is the lightness or darkness of a colour (luminance). I have learned over time that certain colours in nature tend to fall in certain tonal ranges… Reds dark, Greens medium and yellows light. I get messed up most by outlying colours. For example 255 g looks exactly the same as 255 r + 255 g. Anyway, back to my point. When I was younger if I misperceived a colour and somebody corrected me, I could see the colour SHIFT to be the correct colour… my brain was adjusting and compensating. People sometimes think that my perception of colour is dulled down but I perceive a bright orange to be so bright I can’t imagine how it could be brighter. Anyway my 2 cents.

  15. I totally thought this when I was a kid too! I didn’t see the reasoning then, but then this is a completely new chapter to that idea! Thanks for that, it’ll make for an interesting conversation among my philosophical friends 😀

  16. I used to wonder about this exact thing to when I was a kid. I think it started when I had an argument with a friend whether two different colors complemented each other or not.

    My conclusion was that our perception of colors had to be different.

    Always fun to realize you are not the only one having crazy thoughts.

  17. Heh, so, I am not alone in these wonderings…

    When I tried to ask my mom, she could not even understand the concept of the question at first.

    Finally had to word it as “If I could connect Bob’s eye’s to my brain, would the sky still be the same blue as I see it with my eyes?”

    This thought was quickly followed by:
    “what about if his brain was connected to mine?”
    “Can rods and cones work in reverse?”

    I then spent about 6 months trying to make my eyes “create” light.
    At the time, it seemed reasonable to me that since it was a chemical reaction in the rods and cones that generated the signal to the brain that i should be able to make my brain send a signal BACK to the rods and cones and light them up.

    BAck to topic:
    I would think an example of this being true, is people with colour blindness.
    I read somewhere ages ago that the army used to look for colour blind troops and use them as spotters during ww2… the enemy “camoflage” would stand out like a sore thumb to them.
    Don’t know if this is true… one of those many “possible” stories one picks up over the years.

  18. O…M…G!!!When I was young, I tought exactly the same thing!Also, I tought you can’t know if someone is color blind because they don’t know if their green is our red!

  19. WOW! I had the exact same thing in my mind aswell. Tried to reason with a few adults but, eh!

    Also Michael

    For ur question “why only color?”
    1) smells is not as easily comprehended by brain. for example try to recall a nice smell in ur brain. all most people can do is remember a few characteristics as to was it strong, citrus, irritating etc, but for color u can create a colored baloon in ur brain at any time u want. For sound again same logic applies;
    2) texture: same as colour; if ur comprehension of colours change, so would a texture as a direct result of that.
    3) shape: how can shape be comprehended differently? plz explain if u can, I would love to have some mind feed on this.


  20. I had a brain tumour removed some nine years ago and due to damage to the myelin sheath around a nerve controlling movement to one eye I had double vision for a year and a halfs after the main op’ until eye surgery brought me back to single vision. During this spell of double vision I could choose to look at either of two overlapping images of the world produced from each eye and I saw that one eye had a different colour temperature to the other. As a photographer I could ‘see’ that my left eye had an 81a warm up filter on it compared to the right eye,
    in single vision mode these days, the differences between eyes is smoothed out by the brain. I suspect these variations will be as true between different people as between an individuals own eyes and at the end of the day we all live in a slightly different ‘colour space’ but not by much. So red to you is red to me, give or take a little….

  21. I just wanted to say I used to ask the same question. In fact can’t the same question be asked of smell or taste? Perhaps the reason why some people like cabbage is that to them it tastes like chocolate tastes like for me.

    Your first paragraph really sucked me in because you put it almost verbatim the way I have asked it. Thanks for the John Locke notation, I shall now know where to go and do more research.

  22. Hi, Geoff–

    Aren’t eye wonderful? ;^)

    Edwin Land demonstrated that we don’t see color directly because of the wavelengths of light, rather our eyes and brain use the relative characteristics of wavelengths to determine color. Our brain “paints in” the colors in a scene.

    Our eye scans constantly so it can use the relative brightness and contrast of elements in a scene to supply color. That’s why we can see color correctly even when the light source is not full spectrum.

    You might enjoy reading about Land’s experiments and retinex theory of vision.



  23. Hey man, was looking at your DIY laser project and was pondering these prismatic concepts a bit. Before I get into inquiry I would like to applaud you and all our work, the question was surrounded and dissected cleanly …So umm first off, aha, photons and prisms, is our eye like a prism? I can accept the principle of light in a prism, and I can now, after reading your post, semi-understand the concept of our brain creating a “loop”. But what of the object that is pink. Simply does pink paint, or any mixed color, reflect two different wavelengths of photons. Second, look at your skin, its pink in a lot of places. Is this the blue red blood mix? Oh your post is great, a feast for the ponderer. Thanks Geoff

    • Things are bit complicated to get into in the space of this reply, but I’ll do my best! Our eye isn’t quite like a prism – a prism splits apart white light into the photons of different wavelengths making it up, whereas our eye is more of a passive reciever – it simply registers photons of different wavelengths hitting our eye.

      Pink paint, or pink skin, partially reflects white light. It will reflect both blue and red photons (I’m overgeneralizing here a bit but work with me) while absorbing the rest. Your brain then combines those photons in “software” to produce the experience of pink.

  24. It’s comforting knowing that somebody else has thought about this exact same concept. I once tried to explain this same idea to my 7th grade science class, and I might as well have been speaking to the cement wall under my deck.

    I think my colorblind friend first inspired me to think about this. He said that when he saw the color yellow, it looked just like what I considered tan and pink. But when he described “blue”, he would point both to purple and blue, and for green he often pointed to brown. So I always wondered if there was somebody out there that saw what I considered red in the place of, say, blue. I suppose the only possible way for this would be a problem with the color receptors in the brain and eyes?

  25. Finally! I asked myself that very same question some 60 odd years ago … and still don’t know the answer ;-(… At least I was not the only crzy kid asking crazy questions!
    Thanks for a good post understandable by non-specialists 😉

  26. Even for most of the so called “real” colours there’s no way you can go from the colour you see an object to be to the distribution of the wavelengths in the light which is incident on your eye.

    For example if you mix two (idealized) light sources, one at 560and one at 700nm, you’ll see the same colour as if you were looking at light coming off a single source at about 590nm. But in the first case the light that is incident on your eye is equally made up of 560nm and 700nm photons and in the other the light you see is made up of all 590nm photons.

    So saying that only colours that you can generate with a monochromatic source are “real” is fairly silly, because you can generate most of those same colours with a distribution of wavelengths as well.

    I would say either all colours exist only in our brains, or are all colours are “real” depending on you define these concepts.

    Colour we see have a one to many mapping with the distributions of light that are incident on our eyes. In other words, if you see a certain colour there’s no way to know exactly what the distribution of wavelengths in that light is. However, if you are given the spectrum for a certain light source you can work out what colour it will appear as.

    • Hi Andrew – I referred to the monochromatic colors as “real” as they are the only colors that a idealized stimuli from a single photon could reasonably be mapped to, ie they have (in a sense) a counterpart in the “real” world. There are many other stimuli that map to these colors, but those colors are the only ones with this single photon correspondence.

  27. This is a question i have pondered many times as well. Im 16 and I think along the same tracks as you. I beleive that some people’s spectrum may be different as in my blue to them may be their red but we would both call the sky blue still even though if i looked through there eyes i would call the sky red.
    I personaly beleive that its best not to think about it too much as obsession will lead to you going insane. XD

  28. I, too, have thought this about perceived colour. Since I was little, I have noticed how each of my eyes has a tinted colour associated with it: my left eye sees more of a reddish tinge, and my right eye sees somewhat of a greenish one. Considering our light receptors are far from precise, it’s easy to see that different eyes can have different shifts in quantified colour.

    What I like is that your article refers to the brain’s perception of colour. The interpretation of how our brains’ processing of the light that enters our eyes is based on how we come to understand the world around us. I have also often wondered how the world would look through another person’s brain – deconstructed and compared.

    Each of our biologically constructed systems are far cries from being replications. Even identical twins have dissimilar neural connections with dissimilar personalities and propensities. Each of us interprets the world around us via a set of inputs of physical stimuli, but how our brains interpret the data received depends on the construction of our brains and how we have grown to understand our “realities,” and throughout our developmental years of our lives, most of our time is spent trying to make sense of our senses.

    This certainly was an interesting article, and I’m glad there are other people in the world who think about these things as much as I do.

  29. Wow! I always wondered that as a kid! I never knew anyone else did. It’s cool to read about sciences behind some of those “silly” ideas I had as a kid.

  30. Thanks for the post, very good article! I think this is a small piece of a more general question: What is the same thing perceived by other people’s brain? Guess we could never know because in order to interpret what’s in other people’s mind we need to “compile” the information into our own perception.

    Any one interested in that subject could read the 54 pages long paper which argues that colors are real.

    • Hi yoyo –

      Thanks for the link, here’s a excerpt for the interested:

      In other words, is color “out in the world” or “in the brain”? On one side of the debate stand the Objectivists or Realists who hold that colors have objective essences and are properties of physical objects. On the other side stand the proponents of the Illusion theory of color which holds that colors are virtual properties and our perceptions of color are illusory, in that physical objects are not colored, they just appear to be. In this paper we propose taking the philosophy of color realism at face value and using it to develop a scientific theory of color perception. Our approach is based on the ideas of a prominent group of color realist philosophers who identify color with surface spectral reflectances. Influential representatives of this community are Byrne and Hilbert [2] and Tye [3]. We modify their ideas slightly to posit that the physiological, and thence psychological, quantity known as color is the particular model of spectra provided by the sensory apparatus of the human body. We claim then, that all statements about color can be derived from the physical laws underlying spectra and of the structure of the human sensory apparatus.

      Noted philosopher of color Christopher Hardin commented in [4] that: “It is a curious sociological fact that many philosophers, but very few visual scientists, are color realists.”

  31. I had always wondered the same thing, however, its simple and looking into this question so deeply will drive you mad. Its simple, everyone may perceive colors differently, but we have all been “taught” which colors are named the way they are. I look at a block, to me it is green because I was taught that it is green, I may see it completely different than my brother who was also taught that the same block is green. We may all see shades differently, but it is simple to know dark from light and black from white. My perception of the sky may be completely different from yours, there is no way to prove this, we just know that the name of the color of the sky is blue. Why do you think people have different favorite colors? I LOVE blue but others may not perceive it the same and may have more comfort in red or yellow.

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