What is Color? (Synopsis)

You can’t get there by bus, only by hard work and risk and by not quite knowing what you’re doing. What you’ll discover will be wonderful. What you’ll discover will be yourself.” -Alan Alda

Alan Alda recently challenged scientists to explain this simple question to 11-year-olds in less than 300 words. Could you do it?

It seems like a straightforward enough proposition; after all, we surely know it when we see it.
Image credit: Jessica at Ways of Wanderers, via http://waysofwanderers.com/colourful-flower-fields-biei/. Image credit: Jessica at Ways of Wanderers, via http://waysofwanderers.com/colourful-flower-fields-biei/.

But there are some very tight constraints on this contest: you must be a scientist, it must effectively engage and educate an 11 year-old audience, and written/video entries are limited to 300 words/6 minutes, respectively. I've entered a graphic compendium, and I'd love to know what you'd say!

[Go read the whole thing -- formatted for the web (I submitted a PDF) -- over at Medium!]

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Here are two suggestions within the limit of 300 words:

1. “Read the book by Margaret Livingstone, Vision and Art: The Biology of Seeing.”

2. “Ask an artist to explain it; never ask a scientist! (Margaret Livingstone excepted.)”

By far the most important response to anyone who asks "What is colour?" is a reply along the lines: "What a wonderful question! Please tell me why you ask and which aspects of it most fascinate you." In my experience, it is essential to figure out if the questioner is most interested in: how colour vision works; why it came about; or what they can achieve by gaining an understanding of it (perhaps a desire to have career in art or the fashion industry).

You wrote: “What makes one color intrinsically different from any other is the amount of energy it has: for the colors we can see, violet light has the most, while red light has the least.” Sorry to nitpick that statement… While it is correct for individual photon energies, humans are capable of distinguishing: blues and purples even when lit by incandescent lamps having far lower temperature than the circa 5600 K of sunlight; oranges and reds even when illuminated by heavily overcast daylight having a colour temperature of 10000 K and above. There are profound reasons why digital cameras require auto and manual white balance control in order to produce acceptable images of the scenes they capture. The reasons go far beyond photon energies and simple models of human colour vision.

You wrote: “The blue, green and red cones working together even allow us to see colors that aren’t in the rainbow at all, like magenta or pink!” Indeed, easily visible magentas and pinks do not appear in a rainbow because, on the emissive spectra of thermal radiation such as from our Sun, they simply do not exist. Therefore, they do not have equivalent temperature, wavelength, nor photon energy descriptors.

Gaining a thorough understanding of why CMYK is still used in printing (and similar models used by artists), rather than the emissive RGB model used in physics, computer displays and television, would go a long way to answer the question “What is colour?”.

In my opinion, answering this question within 300 words is little different from the challenge of using 300 words to explain to 11-year-olds: “What is the purpose of the Universe?”.

Teaching science is all about having the ability to interact with each individual who desires to learn something. Fewer than 300-word lectures are little more than preaching from a pulpit. The Demon-Haunted World: Science as a Candle in the Dark, by Carl Sagan is a book containing more than 300 words for very good reasons :-) I think this book should be a compulsory element of 21st Century schooling. Well, it's much more fun than the Chaucer I was forced to learn.

By Pete Attkins (not verified) on 01 Mar 2014 #permalink

Ethan's answer contains a category mistake. He explains the physical phenomena that enable us to see colours, but not what colours are. Put another way, the first humans saw colour, and understood the term. But they knew nothing of the physics invoked by Ethan.

A better answer would be that colours are properties of physical objects that we perceive visually. They come in a range of gradations, from blue at one extreme to red at the other. Red is the colour of blood, green the colour of tree leaves in summer...and so on. Philosophers call this kind of definition "showing"—you explain a term by showing how it's used.

By lawrie mcfarlane (not verified) on 03 Mar 2014 #permalink

Color is a subjective sensation that cannot really be explained. Sure you can talk about light and frequency and so on but that is only a small part of the story. So light of a certain frequency hits your retina, and is converted into electrical impulses, but how are those impulses mapped to colors? What is it that makes us experience 450nm light as blue? Do we even experience blue in the same way? Obviously colorblind people don't. Can you imagine a new color you have never seen before? How would it feel to have one's colorblindness cured at age 20?

The interface between external objective reality and it's subjective reflection is so poorly defined and understood. Where does one end and the other begin? Where do our sensations come from? Is the pool of possible sensations limited and independent of biology or is it unbound, our particular senses being tailored by our cellular structure to the specific needs of evolution? Will it be possible one day to implant completely novel senses into our consciousness?

The puzzle of color is inextricably linked to the puzzle of consciousness.

"Ethan’s answer contains a category mistake. He explains the physical phenomena that enable us to see colours, but not what colours are"

You're now making a category mistake.

Colour is not merely the qualia, it is a property of visible light frequencies too.

A prism will ALWAYS split white light out into a spectrum of different colours. You may call one of the colour boundaries in a different place, but the light always splits the same way given the same parameters.

I find that lower middle "29" hard to see. What sort of color-blindness does that denote?

Curious aside: raising my kid, I'm teaching him ROYGBIV. Which means I had to look up Indigo, just to make sure I was describing it right. Turns out, when Newton developed his color scheme what he termed "blue" is what we would term light blue today (like the color of the sky in the last figure, above), and what he termed indigo is just dark blue, like the color standard web browsers use for links. Indigo as a color word has basically fallen out of common usage in English; we just use light and dark blue to describe the two colors now.

I think Ethan's post is valid for what he tried to achieve.

It's pretty simple... if looked from pure physics, color doesn't exist. Only different wavelenghts of EM radiation.

If looked from human perspective.. .color is purely a mental and evolutionary concept. We are wired to perceive it in a way we do. Clearly shown by cases of people suffering from synesthesia. There is nothing physical in green being green.

By Sinisa Lazarek (not verified) on 04 Mar 2014 #permalink

"If looked from human perspective.. .color is purely a mental and evolutionary concept"

So is "solid". And "Temperature".

There's something physical in an emission/absorbtopn spectra of OIII. And we label it "cyan".

A tree leaf is physically there and it has absolutely the characteristics that ensure that it reflects green quite well.

There's something physical about a leaf that makes it green.

This does require light that is green available. But a lack of light is a privative, and they're rather tricky to put down as a real thing. Dark isn't a colour.

"Curious aside: raising my kid, I’m teaching him ROYGBIV"

It probably had a lot to do with numerology. 7 is a nice number numerologically speaking. Indigo's a stupid colour to include, too. And where the heck is brown?

It ought, really, IMO, be Red Orange Yellow Green Cyan Blue Magenta, basing on colours on the same high saturation scale. Brown and Violet are colours in the low-Value end of the scale. Pink is at the desaturated end.

"So is “solid”. And “Temperature”."

yes, and sound as well. Our perception from senses is exactly that.. our. And can't be separated from organ that is associated with it.

Only, color is a the only one where we have different more than 2 "categories".. well maybe taste.... For all other perceptions we have just a gradient of intensity (hot/cold, solid/gas, sound/nosound). Color is a specific sensation where it's not only a gradient of illumination we detect, but actually something more.

Would be cool if we had that ability from other senses as well.

By Sinisa Lazarek (not verified) on 04 Mar 2014 #permalink

I jumped in my own mouth in the previous post... notes are very similar to color.

By Sinisa Lazarek (not verified) on 04 Mar 2014 #permalink

"Our perception from senses is exactly that.. our. "

No, our *specific* response to colour/sound/temperature are ours. That we respond to them with a physical change isn't.

Just because one measure of response is variant in measure between hominids doesn't mean they're specifically solely experienced by them. Some Uni friends were doing philosophy and they made pretty much the same mistake, insisting that, since qualia are personal responses and not the thing itself, that somehow the thing making the perception isn't real.

A tiger can be impressive or scary. But it's still 100% a tiger, and definitely exists.

We can talk about our perception and the physical process that triggered it.

e.g. White as the colour (no such photon exists) and White as a broad spectrum of photon wavelengths at similar intensities.

PS "Dry heat" "Bitter cold". And IR heat can be "seen" by your skin. Colours are made combining three different sensors that happen to be co-located in the eye.

" That we respond to them with a physical change isn’t."

No, we don't all respond to color with a "physical change," so whether someone does or does not is their "property."

Also it's certainly not true that color is just a simple consequence of different wavelenghts of photons hitting retina as countless color illusions show. The same wavelength of light can make you see different colors depending on the image context. The sensation of color is a product of a complex neural process, excitations from retina are only it's inputs.

"No, we don’t all respond to color with a “physical change,”"


The photon at 650nm doesn't cause a change in your retina?

"so whether someone does or does not is their “property.”"

Sorry, no idea what you're talking about here.

"Also it’s certainly not true that color is just a simple consequence of different wavelenghts of photons hitting retina as countless color illusions show."

Yes it is. The blue and red receptors will both activate when impacted by a photon from, for example, ionised OIII.

Your cognitive perception of the colour, what colour you assign that answer can change.

But because you see "white light" as cyan because someone shone a light that was slightly red on something your perception had been set to white, in PRECISELY the same method as "White Balance" in photography doesn't change the reaction of your optics systems.

It only changes the reaction of your visual cortex. That is where qualia reside.

But that never sees a photon.

I think we are all arguing the same thing, yet in different words.

Eye detects light. Sensory rods are tuned to different frequencies/intensities of light.

But color resides in the brain. That's why I argued that perception of color is as much tied to "ourselves" and specifically humans (of course, some animals see color as well, but we are talking about our visual spectra).

The interesting thing is that what we find "pleasing" and how we arrange the color pallet is based on similar if not same mathematics that govern geometry etc.. fibonaci sequence, golden ratios etc...

Is interesting to ponder if something like that would be a quality of all sentient life in universe (regardless of their sensory organs and evolution). Is all sentient life wired to find same mathematical concept beautiful, or is it just us?

By Sinisa Lazarek (not verified) on 05 Mar 2014 #permalink

"I think we are all arguing the same thing, yet in different words."

Possibly arguing about different *things*, but where language gives them much the same meaning.

Colour doesn't reside in the brain if you consider colour a mix of photons. sRGB does.

The colour gamut of print is different from the colour gamut of a photoemitter like phosphor VDUs. Or for OLEDs. However, the colourspaces (including colour spot values as per Kodac) are able to manage a mapping from one to the other.

"The colour green" as perceived by two different people may have a different colour gamut, but people are making something out of the difference when it's really just a fact that we don't have access to the colour space gamut available to a human brain.

But OIII emission will be of a particular colour, even if you're colourblind.

If you've ever used calibration software that comes with your printer and VDU (nobody ever does), you're changing the colour response in just the same way as some philosopher says SL's "green" is different from my "green".

Philosophers never even notice there's a calibration software tool in their driver pack...

"Is all sentient life wired to find same mathematical concept beautiful, or is it just us?"

For things like fibonacci numbers, they are a consequence of non-design in the process. All that's needed to replicate a system is knowledge of "nearest neighbour" properties and a consistent single premise of growth.

Bingo, fibonacci series.

So it seems likely that any other organism, growing up in a world that isn't designed, would grow up seeing such series and finding they comport with expectations (therefore pleasing: having ones face eaten off often offends. It's not expected and therefore extremely rude!).

Golden ratios don't have as easy a description in chemistry (the basis of biological organisation), so it's less certain their existence will seem pleasing, but there's nothing about "us" in the definition to make it beholden to humans to perceive it to be pleasing.

Whether red is a hot or warning colour or blue a calm, cool colour is much more tied to what evolved and therefore likely to be specific, if not to humanity, to biology as it developed here on earth.

1. colorblindness
2. look up Fechner color illusion

@ Wow

I only disagree with this "But OIII emission will be of a particular colour, even if you’re colourblind."

They will of a particular wavelength, but no color.. if you have no cappacity to see it... thus a color blind person won't see cyan.. or a species whos eyes/brains are wired differently might see .. whatever...

By Sinisa Lazarek (not verified) on 06 Mar 2014 #permalink

"They will of a particular wavelength, but no color."

Then you'd claim that until you see an elephant, it doesn't exist..?

At least we know your answer to the "If a tree falls in a forest" query!

This isn't that you're *wrong*, you're considering something different from me as reality.


1) look up "teach your grandmother to suck eggs"
2) Absolutely doesn't answer the obscurity of your statements queried, rather pretends that all the "problems" are me, without actually pointing out what that problem, as you perceive it, to be.

"Then you’d claim that until you see an elephant, it doesn’t exist..?"

no, of course it exists. this isn't about that. Like you said, OIII will emit light. That's the fact. But weather an observer will see it as white light, or grey, or cyan, fluorecent pink with spots, or see it at all, is entirely dependant on it's brain/eye evolution and not on physics.

By Sinisa Lazarek (not verified) on 06 Mar 2014 #permalink

Therefore color is a qualitative property that our visual/neural system ascribes to different frequencies of EM. That's not the same as saying EM doesn't exist if we don't see it.

By Sinisa Lazarek (not verified) on 06 Mar 2014 #permalink

Sorry, this will be final one.. But just thought a better way to phrase it. Maybe this will help clairify my argument.

The physics of light ends when the photon reaches the neural receptor. What happens next is down to our brain. Weather we "see" or "hear" or "smell" that photon... this is evolution. Not the fundamental property of light. Because that impression will be different in every species.

By Sinisa Lazarek (not verified) on 06 Mar 2014 #permalink

To challenge scientists to explain a simple question to 11-year-olds in less than 300 words, what is that a challenge?

This rather smells of white wise bearded men who have nothing better to do and entertain each other with mental garbage which only the self-proclaimed scientist can believe that a 11-year-old MUST understand.

How about teaching the 11-year-olds how they themselves can explain and defend knowledge, on the schoolyard, in the classroom, on the street, at home. Why is it that I suspect that this is a real and not a fake challenge for self-proclaimed scientists?

By Chaeremon (not verified) on 07 Mar 2014 #permalink