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Comment by BrandoElFollito | Hacker News Reader

The first one would be "colors exist as a physical concept". They do not.

There is no relationship between the physical nature of light and what we call "color". A wave has a frequency. There is no concept of "color" associated to a wave.

We statistically put names on some convoluted detector/brain transformations and everyone does the transformation differently. This is why most of the people agree that a tomato is "red".

As an ex-physicist, I hate to speak about colors in a physical context (and yes, we have charts that show that higher frequencies are "blue" and lower ones "red"). Color is a biological concept and should stay that way.

And then, as a farther, I have to explain to my children the convoluted course on colors in high school in France.

Sorry, I had to let off some steam.

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This is navel gazing along the lines of cocktail-fueled debates over a tree falling in a forest. Does light still have a color if no one is around to see it?

Fundamentally these words have lots of reasonable wiggle room to expand or narrow their definitions. Still, lots of technical domains would like to be explicit about what is meant, especially when reusing common words, which is why man invented the glossary.

Unfortunately this hasn't stopped endless argumentation over whether a tomato is a fruit or a vegetable. For whatever reason, it's often presumed that the definition of fruit used in botany has "won", even though botany has nothing to tell us about what a vegetable is or how to distinguish one from a fruit.

I am not sure I understand your point.

On the one hand you have light waves that hit some receptors in the eye. These receptors (various kinds) sensitive to frequencies according to a function. This creates a specific signal that is analyzed by the brain which assigns a "color" to that signal.

Everyone's, to some extent, functions are different. There is a general trend so most people agree on "colors". When you are colorblind, the functions differ drastically (or are just flat).

This is why "color" is a biological concept (same as, say, "pain") to which we are desperately trying to attach three or four numbers (or, worse, a wavelength)

450 THz electromagnetic waves are unambiguously red light, you can nitpick about the shade of red, how people perceive it, etc... but it is red. It may look differently to colorblind people, or dogs, but it is red. The electromagnetic spectrum of frequencies just lower than red is called infra-red, don't tell me that physicists don't talk about infrared.

If you look up some colors in Wolfram-Alpha you will have precise ranges of frequencies, I am not sure they are officially defined ranges, but colors, at least pure colors correspond to physical quantities.

There is some overlap with biology, and there are some colors are special (brown, purple, ...) and can't be defined by a single frequency. Then you can introduce color perception, and how very real and physical red photons are perceived as red, why a combination of red and green photons are perceived the same way as yellow photons and how spectrometers reveal the difference, and how there are no purple photons.

Composite colors are a bit more complicated, you need to add a bit of math (namely, a color space) in order to formally define them from physical quantities, but saying that it is not a physical concept is going a bit far.

No need to make physics more abstract than it is. Because what's next? Temperature is not a physical concept because we don't all agree on how hot something is? Like color, temperature is a well defined physical concept that is based on our perception.

In that case, what is the frequency of the light needed to create "salmon"?

Or in other words: is "salmon", "fuschia" and other colors located on the frequency spectrum? If so - why do we have zillions of color spaces instead of just a simple frequency? (or wavelength)

At the moment when you introduce color spaces, you start accounting for how our eye receptors are sensitive to frequencies and leave the realms of physics (mostly because the receptors differ from person to person)

When you take a 450 THz wave, you say it it is "unambiguously red" because it is what happens to be the word for the signal which is triggered by that wave. In most of the people. Roughly the same way.

What I am trying to say here is that a color is a concept as well defined as "pain". You can have all sorts of measures, but none is strict.

Finally, there are no "red photons", or green or blue (you mention them) - this simply does not exist at all as a concept.

I think with color, it’s important to appreciate the irregularity that exists in this domain. You’re right that colors are defined as ranges of wavelengths or blends of ranges of wavelengths. And so there is a mathematical component to color. Yet, the mathematical view of color is imperfect if you ultimately are concerned with the perceptual end result. People are always trying to create better, more perceptually accurate color spaces, but all of them have their issues and weird corners where the adjusting the values in a certain direction doesn’t yield the expected result.

> A wave has a frequency. There is no concept of "color" associated to a wave.

Funny because when I explained radiant heat to my daughter I used it as an example of light, but infrared is a color we can’t see (but we can feel the light the same way we feel the sun on our skin). She asked about other colors and I went into ultra violet, X rays (a color to which we are transparent), gamma rays, and so on.

Yes, you described her how a wave interacts with her body and creates sensations (heat, colors, ...).

This is absolutely true, but the wave does not carry any of these sensations on its own, it is its interaction with sensors/receptors in her body that creates it.

Like I said elsewhere, a color is like pain - a needle does not have any "pain" in it and a couch hit with a needle will not create "pain".

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