What is color?


Vort
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What is color?

 

Most people would say it's a property of substances. Butter is yellow, the sky is blue (or gray, if you live in Seattle), bears are brown, clouds are white (or gray, if you live in Seattle). This is the "pigment" model of color: If you want green paint, mix blue and yellow.

 

This is actually a pretty robust model. The problem is that it fails to explain color perception in the organism. If we want to understand what it means when we see a color, it's not sufficient just to say, "Well, that's the color of that thing."

 

As we dig deeper to figure out what "color" is, we find another, more powerful, model for color, the one physicists use: Color is a measure of the wavelength of visible light. Thus, "red" light is light of a wavelength within a certain range, as is "blue" light and "violet" light and "yellow" light and  "green" light and so forth. In fact, once you learn the "rules" for combining light wavelengths to make other colors (similar but not identical to those for pigments), this model becomes even more powerful than the pigment model.

 

Except there's a huge, gaping hole in this whole theory. If light "color" corresponds one-to-one with light "wavelength", why should combining "red" light with "green" light give you "yellow" light? What you have is red and green, with red and green wavelengths. Those two types of photons do not magically combine into brand new, yellow-colored photons.

 

This observation points the way to a real consideration of what color actually is, which is surprisingly simple: Color is a perception by your brain based on signals from your retina.

 

The reason you see color is because your eyes' retinas have a special type of color-sensitive cell, called a "cone". These cones come in three flavors, each tuned to a certain range of wavelengths: magenta (red), cyan (blue), and green. In reality, each type of cone is sensitive to a large range of wavelengths, so there is lots of overlap between all the cones; but each type of cone is most sensitive to its corresponding "color".

 

So if we see some "pure yellow" light, in the physics sense -- that is, for example, light with a wavelength of 580 nanometers -- the color-sensing cones in our retinas (R for magenta or red cones, G for green cones, B for cyan or blue cones) output something that looks like this:

 

R: ++++++++

G: ++++++++

B: ++++

 

So here's the key to color! If we can produce the above sensation in an eye, BY ANY MEANS, that eye will see yellow! So what if we show red (magenta) light and green light together? (Remember, the blue-sensing cones will react to some extent, even though they are not "tuned" to those wavelengths.) In such a case, we might well get a profile that looks like this:

 

R: ++++++++

G: ++++++++

B: ++++

 

Well, well. Whaddya know? Looks like the above profile! (Because I copied-and-pasted it...) So now we know why, on a computer monitor, the "yellow" is actually just red and green. It's all a matter of getting our retinal cells to respond according to a profile. There is no actual "yellow" light there, but that doesn't matter.

 

This is the big challenge currently being fought with LED light bulbs: How do you "tune" the light bulb so that it looks like it's giving off "white" light? True "white" light is a more or less even blend of all visible wavelengths, continuously distributed throughout the spectrum. But LEDs don't show a spectrum; they show only ONE wavelength of light (actually, a very narrow band of wavelengths). So the trick becomes, how can you combine  various colors of LED, which output various discrete wavelengths of light, to mimic the effect of white light in the human eye?

 

There are at least two major problems with this:

  1. Light that reflects off of various colored surfaces can be changed depending on the wavelength, with some wavelengths being reflected better than others and some absorbed more than others. Thus, even if the light coming off the LED bulb looks "white" to our eyes, objects illuminated by that light might look really weird-colored, not normal at all, because they are not really being illuminated by a continuous spectrum.
     
  2. Different people's retinas have slightly different tunings for the color cones. In fact, the odds are that your two eyes have slightly different tunings from each other, so that you don't see colors quite the same in your left eye as you do in your right eye. So it becomes impossible to select just a few diode wavelengths to produce a white-looking light that looks good to all people.

So what has this to do with this list? Nothing, really. I just thought it was interesting. I have a degree in physics and a fairly deep background in biology, yet it took me many years of pondering this to figure this out. (I'm not the brightest LED in the chandelier.) I'm sure this has been understood for a hundred years, but I only realized it maybe ten years ago, maybe less.

 

I do think this has great philosophical value, though. In fact, I think the principle involved is directly applicable to much of what we see in society, in philosophy, in religion, and in our own lives.

Edited by Vort
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So what has this to do with this list? Nothing, really. I just thought it was interesting. I have a degree in physics and a fairly deep background in biology, yet it took me many years of pondering this to figure this out. (I'm not the brightest LED in the chandelier.) 

 

Thank you for using LED's :)

 

 

 

I'm sure this has been understood for a hundred years, but I only realized it maybe ten years ago, maybe less.

 

I've understood this since high school, but only because my Physics teacher made a point of teaching that color is a set of wavelengths.  He was insistent that color was not an inherent property of any object, but that the way an object interacted with the wave lengths was.

 

I believe he also opened the can of worms of whether or not each person perceives the same wavelengths the same way.  My retina may see blue when yours sees orange.  But we've been trained to associate color with objects, so we both call it green.  That part took me a few years to grasp, but it was a fun exercise at the time (as was my physics teacher's love of driving nails through boards with his bare hands)

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When I was small I was introduced to the pigment mixing paint model of color. Then my parents told me white was all colors, but for some reason I could only mix gray.

Gray is almost white. It's when you mix white and black together...or red, blue, and yellow... Lets just say, to this day I have yet to successfully mix a perfect white value. The closest I can get to mixing white is gray.

Even knowing what white is, via physics and light waves and the responsiveness of the eye to light...I still haven't been able to do it.

It reminds me of this verse in Isaiah. Even knowing what righteousness is, we still can't quite mix the colors of godliness together and come out with clean garments.

 

 

 

Isaiah 64:6
But we are all as an unclean 
thing, and all our righteousnesses are as filthy rags; and we all do fade as a leaf; and our iniquities, like the wind, have taken us away.

Christ isn't like bleach, it's a new can of paint  ;)  :P  :D

[it's a parable, so yes I understand that there is a physical reason for the mixing of paint not working]

Edited by Crypto
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What is color?  (...)

 

  1. Different people's retinas have slightly different tunings for the color cones. In fact, the odds are that your two eyes have slightly different tunings from each other, so that you don't see colors quite the same in your left eye as you do in your right eye. So it becomes impossible to select just a few diode wavelengths to produce a white-looking light that looks good to all people.   (...)

 

 

But thanks to God we only have one brain.  :P 

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Pretty sure the best and most accurate answer to that is, "Yes".

I am sorry, this is probably actually off topic. It's not physics.

 

but....

I mean the experience. Obviously we describe approximately the same wavelengths as "red". But the actual experience of seeing red... Beyond even the differences in our eyes (I can observe differences in my own, one is more fully saturated than the other, I hope that doesn't mean one of my eyes is going bad) and the pretty intense processing our brain does to the images sent to it by our eyes.

The experience of seeing red, I think, must vary from person to person. Eliciting emotions and feelings and memories that are different.

My experience, is different, unique even, when viewing each color.

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I just came from another thread called "The Worst Joke Forever and Ever," and since I landed here...

 

Did you hear about the two cans of paint that got married?  A few months after that, the female can of paint said to the male can of paint, "Darling, I think I'm pigment."

 

Back to topic: Some researchers think that humans originally had only two words for color: black and white.  As they saw more things around them, they slowly added new colors over time.  Red for blood, then green for plants, then yellow for...  well, um, let's stop there.

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The spectrum of light we can see is quite small in comparison to the full spectrum of light. I.e. the predator in the movie with Arnold Schwarzenegger could see infrared. And what about x-ray? Or if we could see electromagnetig waves - what kind of a world would we see? A world surrounding us full of colours, phenomenally changing colours, and our brain would have to grow up to the size of a basketball just to interprete all these impressions. Not much place for thinking. That's why we only can see a small spectrum of the light and its colours.

 

I've heard that cats can only see black and white. But see how happy they are when they have enough food and they can lay on your chair. This proofs that happyness doesnt't depend on the quantity of colours you see. It's only important, as given by the example of a cat, that a well tasting fish can be distinguished from a clothes peg. Cats don't have fine noses, dogs have, so cats have to explore and to see the world with their eyes. But black and white seeing as a visual ability seems to be enough. Do we really need colour TVs? I would say no. Not for the reason to be happy.  smiley-eatdrink062.gif

Edited by JimmiGerman
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I just came from another thread called "The Worst Joke Forever and Ever," and since I landed here...

 

Did you hear about the two cans of paint that got married?  A few months after that, the female can of paint said to the male can of paint, "Darling, I think I'm pigment."

 

 

Male can: "This must be a figment."

Edited by JimmiGerman
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Forget what is color... just please find a way to get my husband to understand that fuchsia is not pink and that schoolbus yellow is a specific color which is different from sunflower yellow.

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When I was small I was introduced to the pigment mixing paint model of color. Then my parents told me white was all colors, but for some reason I could only mix gray.

Gray is almost white. It's when you mix white and black together...or red, blue, and yellow... Lets just say, to this day I have yet to successfully mix a perfect white value. The closest I can get to mixing white is gray.

 

The reason you can't get white by mixing different colors of paint, but only gray or black, is because of how paint colors work. When white light bounces off of orange paint, what is in that reflected light? Only wavelengths that make our eye see orange; to oversimplify, only orange wavelengths. Similarly, if you have purple paint, it reflects the purple wavelengths and absorbs the others.

 

So what if you mix orange and purple paints together? Well, the orange paint will absorb all but the orange wavelengths, and the purple will absorb all but the purple wavelengths, leaving you with...

 

...nothing.

 

Now, of course, the paint pigments don't really absorb ALL other wavelengths. They reflect some of it; they just heavily bias the spectrum in favor of "their" color. So you don't automatically get black (no reflected light) from mixing different pigments, but you do get some sort of gray.

 

White paint requires maximum reflectivity. I think much white paint contains a titanium oxide to give it the brilliant white reflectivity.

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The real question is, is my red the same as your red?

 

Pretty sure the best and most accurate answer to that is, "Yes".

 

Not necessarily. Being color blind/deficient I will look at something and say it's red and my kids will say "Dad, that's green."

Just because I see it differently does that mean I am wrong? Maybe I'm right and everyone else is wrong :D.

 

Is it any different than two people tasting something and having different descriptions of how it tastes? 

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The reason you can't get white by mixing different colors of paint, but only gray or black, is because of how paint colors work. When white light bounces off of orange paint, what is in that reflected light? Only wavelengths that make our eye see orange; to oversimplify, only orange wavelengths. Similarly, if you have purple paint, it reflects the purple wavelengths and absorbs the others.

 

So what if you mix orange and purple paints together? Well, the orange paint will absorb all but the orange wavelengths, and the purple will absorb all but the purple wavelengths, leaving you with...

 

...nothing.

 

Now, of course, the paint pigments don't really absorb ALL other wavelengths. They reflect some of it; they just heavily bias the spectrum in favor of "their" color. So you don't automatically get black (no reflected light) from mixing different pigments, but you do get some sort of gray.

 

White paint requires maximum reflectivity. I think much white paint contains a titanium oxide to give it the brilliant white reflectivity.

I am aware of this lol. It's just that no matter how much you try to mix paint to get white, you can't do it that way. And gray is a step closer to white than say Blue is anyway. (at least imo)

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My wife will call things I swear are black "blue". Navy blues that are so dark that you have to be out in the full force of daylight to see the blue don't get to be called just "blue". "midnight blue" or "navy blue" but when you say blue, I don't look for things that are pretty much black.

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What is color?

 

Most people would say it's a property of substances. Butter is yellow, the sky is blue (or gray, if you live in Seattle), bears are brown, clouds are white (or gray, if you live in Seattle). This is the "pigment" model of color: If you want green paint, mix blue and yellow.

 

This is actually a pretty robust model. The problem is that it fails to explain color perception in the organism. If we want to understand what it means when we see a color, it's not sufficient just to say, "Well, that's the color of that thing."

 

As we dig deeper to figure out what "color" is, we find another, more powerful, model for color, the one physicists use: Color is a measure of the wavelength of visible light. Thus, "red" light is light of a wavelength within a certain range, as is "blue" light and "violet" light and "yellow" light and  "green" light and so forth. In fact, once you learn the "rules" for combining light wavelengths to make other colors (similar but not identical to those for pigments), this model becomes even more powerful than the pigment model.

 

Except there's a huge, gaping hole in this whole theory. If light "color" corresponds one-to-one with light "wavelength", why should combining "red" light with "green" light give you "yellow" light? What you have is red and green, with red and green wavelengths. Those two types of photons do not magically combine into brand new, yellow-colored photons.

 

This observation points the way to a real consideration of what color actually is, which is surprisingly simple: Color is a perception by your brain based on signals from your retina.

 

The reason you see color is because your eyes' retinas have a special type of color-sensitive cell, called a "cone". These cones come in three flavors, each tuned to a certain range of wavelengths: magenta (red), cyan (blue), and green. In reality, each type of cone is sensitive to a large range of wavelengths, so there is lots of overlap between all the cones; but each type of cone is most sensitive to its corresponding "color".

 

So if we see some "pure yellow" light, in the physics sense -- that is, for example, light with a wavelength of 580 nanometers -- the color-sensing cones in our retinas (R for magenta or red cones, G for green cones, B for cyan or blue cones) output something that looks like this:

 

R: ++++++++

G: ++++++++

B: ++++

 

So here's the key to color! If we can produce the above sensation in an eye, BY ANY MEANS, that eye will see yellow! So what if we show red (magenta) light and green light together? (Remember, the blue-sensing cones will react to some extent, even though they are not "tuned" to those wavelengths.) In such a case, we might well get a profile that looks like this:

 

R: ++++++++

G: ++++++++

B: ++++

 

Well, well. Whaddya know? Looks like the above profile! (Because I copied-and-pasted it...) So now we know why, on a computer monitor, the "yellow" is actually just red and green. It's all a matter of getting our retinal cells to respond according to a profile. There is no actual "yellow" light there, but that doesn't matter.

 

This is the big challenge currently being fought with LED light bulbs: How do you "tune" the light bulb so that it looks like it's giving off "white" light? True "white" light is a more or less even blend of all visible wavelengths, continuously distributed throughout the spectrum. But LEDs don't show a spectrum; they show only ONE wavelength of light (actually, a very narrow band of wavelengths). So the trick becomes, how can you combine  various colors of LED, which output various discrete wavelengths of light, to mimic the effect of white light in the human eye?

 

There are at least two major problems with this:

  1. Light that reflects off of various colored surfaces can be changed depending on the wavelength, with some wavelengths being reflected better than others and some absorbed more than others. Thus, even if the light coming off the LED bulb looks "white" to our eyes, objects illuminated by that light might look really weird-colored, not normal at all, because they are not really being illuminated by a continuous spectrum.

     

  2. Different people's retinas have slightly different tunings for the color cones. In fact, the odds are that your two eyes have slightly different tunings from each other, so that you don't see colors quite the same in your left eye as you do in your right eye. So it becomes impossible to select just a few diode wavelengths to produce a white-looking light that looks good to all people.

So what has this to do with this list? Nothing, really. I just thought it was interesting. I have a degree in physics and a fairly deep background in biology, yet it took me many years of pondering this to figure this out. (I'm not the brightest LED in the chandelier.) I'm sure this has been understood for a hundred years, but I only realized it maybe ten years ago, maybe less.

 

I do think this has great philosophical value, though. In fact, I think the principle involved is directly applicable to much of what we see in society, in philosophy, in religion, and in our own lives.

I tend to fall under the "various EM wavelengths" type.

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  • 8 months later...

What is color? ...

I do think this has great philosophical value, though. In fact, I think the principle involved is directly applicable to much of what we see in society, in philosophy, in religion, and in our own lives.

Although it has been nearly nine months since the OP, I wonder if you would be interested in elaborating. It's interesting. :)

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Although it has been nearly nine months since the OP, I wonder if you would be interested in elaborating. It's interesting. :)

 

It's worth noting that certain psychoactive drugs, e.g. LSD, can cause your retina to fire in an odd way (or your brain to perceive it as having so fired). Normally, when you see "pure green" light, it will maximally stimulate your "green" cone receptors, and only minimally stimulate the others:

 

R: ++

G: ++++++++

B: ++

 

So this is what we call "pure green". The red and blue receptors fire, but only at a minimal rate. And remember: That's with "pure green" light, the color that will maximally stimulate green while minimally stimulating red and blue.

 

So what if you suddenly perceive your cones firing like this?

 

R: [nothing]

G: +++++++++++++++

B: [nothing]

 

Then you see a "color" that is impossible to generate normally. You see a green that is "so green that it's impossible". And it really IS impossible, normally, because there is no color that can cause your cones to fire like that. It is not a normal, "honest" sensory effect, but is drug-induced.

 

Recall Joseph Smith's testimony of the appearance of Moroni to him. He said that "[the angel Moroni] had on a loose robe of most exquisite whiteness. It was a whiteness beyond anything earthly I had ever seen; nor do I believe that any earthly thing could be made to appear so exceedingly white and brilliant." (JS-H 31) What was going on here, from a biophysical perspective? Well, we don't know. But we might conclude that the sensory impressions caused by a "supernatural" (no such thing, but you know what I mean) resurrected being are just completely different from any normal impression. Or maybe there is a spiritual addition to our physical vision that we normally don't perceive but that overrode Joseph's perceptions in this case. Or maybe something else.

 

The fact is that almost everything we think we "know" is really a memory of our physical impression of something. Since our physical senses can be deceived, we literally cannot always "believe our own eyes". Having the same impression at various times seems to make us more likely to believe, to think we know. But honestly, I would have bet my house that the dress was cream and gold. All you had to do was look at it. Duh.

 

Spiritual "knowledge" is unlike that. It is somehow "deeper", though I don't really like that word. I do think that we are prone to spiritual deception, just as we are to physical deception. But I think the nature of that deception differs; I believe that if we are sufficiently prepared, we cannot be spiritually deceived. Thus, we can know things in a much more sure manner than, for example, the scientist "knows" about gravitation or evolution or energy states.

Edited by Vort
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Yes, I think those applications are quite useful to me personally. I think there are more applications, too. For example, it has already been mentioned that people don't perceive the same color (and many or most people may not even perceive the same color with both eyes). Yet most people, I daresay, will insist that what they "see" is the way it is. Some people are unable (or unwilling) to concede this, and they insist that what they see is somehow superior to what others claim to see (or won't or can't see). This is demonstrated repeatedly in eye-witness accounts of auto accidents, in religious arguments, with philosophical differences, etc. I think it has application as well in helping us (if we wish to internalize the lesson) to empathize, and to understand one another better than we might otherwise be prone to do.

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...What you have is red and green, with red and green wavelengths. Those two types of photons do not magically combine into brand new, yellow-colored photons.

I had not pondered this in a photon model.  But in the wave model of light, this actually does happen.  The light energies are combined into a new unique wavelength through superposition.  I don't see how that would result in anything different with the photon model.
 

This observation points the way to a real consideration of what color actually is, which is surprisingly simple: Color is a perception by your brain based on signals from your retina.

 

I do think this has great philosophical value, though.

So if a tree falls in the forest with no one around to see, does it still have green leaves?

 

but seriously, folks...

 

As you brought in the discussion about cones, this doesn't really work.  The interaction of light with the different cones is much more complex than what you described.  And when you consider the different types of color blindness and the perception of colors that some animals possess which exceed ours, this "definition" is largely a matter of opinion.

 

But LEDs don't show a spectrum; they show only ONE wavelength of light (actually, a very narrow band of wavelengths). So the trick becomes, how can you combine  various colors of LED, which output various discrete wavelengths of light, to mimic the effect of white light in the human eye?

No, they've combined LED tech with fluorescent tech and developed a quasi spectrum emission.  That is why the bright white LED lights have that bluish hue that is characteristic of fluorescent bulbs.
 
In the end, you have two definitions of what color is:
 
1) Certain configurations of electromagnetic waves.
2) Our perception with our eyes.
 
The first is scientific, exact, measurable, and dependably reproducible.  The second is ... not.
Edited by Guest
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I think another facet of the philosophical application exists in that light isn't precisely like anything else we experience. In this thread mention has been made of the wave-like characteristics of light. And the thread has touched on the particle-like characteristics of light, although not quite as much. As far as I'm aware, however, nobody has successfully described both characteristics simultaneously to everyone else's satisfaction. I have tried to conceive of a model that incorporates particles behaving as waves (and vice versa) but I can't even satisfy myself. And then for me at least there is that pesky set of questions which leaves me feeling somewhat like Orwell's literary character, Winston Smith--I am wont to say that I understand how but I do not understand why. It seems the only solution is to do as (I think) modern scientists do and just choose to accept wave-particle duality...for now anyway.

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Why can't we mix paint colors together to get white?

Vort explains this fairly comprehensively a few posts back, shortly after the one I made.

To simplify:

Pigment, or paint absorbs all colors but the one it reflects. When you mix paints it begins to absorb most all wavelengths of light, which our eye will perceive as dark or black.

Edited by Crypto
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