
Tetrachromats: people who see colors invisible to most of us (2014) - jakub_g
https://www.bbc.com/future/article/20140905-the-women-with-super-human-vision
======
andrewl-hn
My spouse is a tetrachromat, and it's fascinating. Sometimes she sees patterns
on leafs or bird feathers that other people don't see. Sometimes she can
detect a very minor difference in colors of clothing items that other people
see as identical. If a person wears those two items of clothing together she
finds it really irritating.

She also sometimes see colors in her dreams that are outside of a pallet
humans see in real life, but after she wakes up she can't describe them. It's
not one color or one hue, there are several colors that she can only
experience in her dreams.

~~~
arketyp
I don't see why seeing an extended pallet in dreams would be a thing
particular to tetrachromats. Unless trichromatic vision completely covers the
gamut of naturally occuring wavelength combinations, which I doubt.

~~~
roywiggins
Colors like magenta (red and blue wavelengths together) are nonspectral,
having no single wavelength they correspond to. They only exist as a mix, and
we see a pinkish color that you can't write down as a wavelength.

Tetrachromats could plausibly see more nonspectral colors by activating their
extra color receptor and one of the other ones. There would be no exact
equivalent in trichromatic vision.

It depends on what their brains decide to do with it- maybe they would just
land on an existing color in between. But there's no reason it _has_ to.

So these colors are something that tetrachromats could maybe see while awake,
but usually with lots of other colors mixed in. Asleep, maybe the brain starts
to play with them and generates pure versions of them. Trichromats wouldn't be
very likely to have these dreams because their brains don't have experience of
tetrachromat nonspectral colors at all.

~~~
_nalply
Ah! Now I have theory: We trichromats have a hue circle, and magenta is the
point where the lower and higher wavelenghts are joined. However this simple
model breaks down for tetrachromats. Perhaps they have two hue circles
orthogonal to each other. This means, hue becomes two-dimensional. Really
crazy to imagine such a thing.

I imagine in school the teacher tells the poor girl: Mix the blue and yellow
colors to get green, and the girl doesn't understand because she has a lot
more complex color model than the teacher.

~~~
roywiggins
Here's a badly-worked out theory.

We see magenta as a separate color because we can distinguish it from green-
it's not green, because Red and Blue don't activate our green cones. But we
can't distinguish between spectral yellow and R+G because there's no yellow
cone: the activations of all our cones are more or less identical in both
cases.

If you have a yellow cone, you'd conceivably be able to distinguish between
both kinds of yellow: redgreen and yellow _could_ look as different as green
and redblue do. I'm not sure how that would look as a "wheel", perhaps a
figure-eight with the crossing at yellow.

~~~
marvin
I think this is a very good explanation. You're emphasizing that a trichromat
will experience the same activation of their cones to the wavelength of yellow
light, and light containing the wavelengths of red and green mixed. So the
spectra of these two colors will be different, but appear identical.

Whereas a hypothetical tetrachromat with an additional cone type that
activates to the yellow wavelength, will have obviously different activations
of their cones for the "wavelength of yellow" and "wavelengths of red and
green mixed". And hence experience them as different colors.

I'm not familiar enough with the different definitions of color spaces to
define how to model this. You could easily define it as a four-dimensional
RGBY color space, but to my understanding the other color spaces are defined
because they have better properties for combining different colors, or playing
better with interpolation between colors.

It would be a challenge to come up with a good four-dimensional color space
that is a useful artistic and visual tool, given that there are very few
people around to evaluate it! And also because all computer monitors are
trichromatic, so it'd be a job in itself to set up a test system.

I wish someone in the interview had asked some of these people how they
experience photos on computers!

~~~
jtolmar
You can arrange the three colors in a triangle, which defines a plane, is
treated like a circle in color theory, and looks like a weird stretched out
"U" when put in a perceptually uniform space (stretched towards green, which
we see best, and flat on the magenta side). Perceptual color spaces combine
this with luminance, which is sensed by rods instead of cones.

Tetrachromatic colors could be placed in a tetrahedron, defining a space and
being approximated as a sphere. A perceptually uniform representation would
probably be curved on the three edges that agree with the spectrum and flat on
the three that don't. Green is still probably the biggest. Then you'd add
luminance as a fourth dimension because it's still rods.

~~~
marvin
Great explanation, thanks :)

------
raphlinus
There's actually a way for us to experience something similar: wear eyeglasses
where the two lenses have different spectra. Then these "extra colors" show up
as a shimmering sensation.

I have such a pair, but have to say it's not very exciting; there's not that
much metamerism in the real world.

~~~
OscarCunningham
This is a really good idea. In fact it should be able to promote trichromats
to hexachromats, since we have two eyes. I wonder if we could calculate
optimal filters, sort of like EnChroma (enchroma.com) for trichromats.

Where did you get your pair? What filters did they have?

~~~
raphlinus
It was many many years ago, so I unfortunately don't have the details. But
yes, the process should be quite similar to EnChroma.

------
bhauer
Maybe if this group grows over time we can finally move past the 24-bit color
space that the mainstream has been stuck with for decades. I'm not a
tetrachromat nor a woman, but I do routinely find myself bothered by the
banding of gradients in the 24-bit color space. I went as far as asking
Mozilla to consider adding a dithering algorithm to their gradients [1].

[1]
[https://bugzilla.mozilla.org/show_bug.cgi?id=627771](https://bugzilla.mozilla.org/show_bug.cgi?id=627771)
(note the linked example is from 9 years ago and the -moz-linear-gradient CSS
attributes no longer work.)

~~~
BurningFrog
I think that is entirely separate.

The 24 bits are 3x8. To accommodate tetrachromats, you'd go to _4_ x8, not
3x10.

~~~
pedrocr
I don't think there's any need to go to four primaries. If you keep just RGB
but have more bits per channel you can widen the color space without getting
banding while also representing many more colors. You just move the RGB
primaries out to cover more space. Doing 3x32bit float is common to get you
all the color resolution you'll ever need for calculations in image pipelines.

~~~
pygy_
We could even go up to 2x64bit floats for even more definition...

Wait, that didn't make sense to you as a trichromat?

Neither does your suggestion to a tetrachromat. For them color is a four
dimensional space (tetrachromat literally means "four-colorist"). The RGB cube
becomes a RXGB hypercube. You can't emulate X with RGB like you can't emulate
green with red and blue.

~~~
pedrocr
That will heavily depend on if the extra primary actually allows you to sample
something significantly different from the other three or just gives you more
color differentiation. My understanding was that human tetrachromats had their
extra primary close to one of the "standard" ones and that gave them more
color differentiation but not exactly extra colors.

~~~
masklinn
It gives them more color differentiation in the same way your trichromacy
gives you more color differentiation than a deuteranope.

------
neilwilson
My daughter has something like this. She can see colours nobody else can, but
pays for it a little by not being able to see as much out of the corner of her
eyes than most people.

One optician panicked so much at what she said they referred her to the
hospital in case she was having a stroke! And that's when we discovered what
she can do. I just thought she was good at picking clothes that went together
well.

~~~
goto11
> I just thought she was good at picking clothes that went together well.

Good for her, but I doubt this is because she can "see colors nobody else
can". If that was the case, she would most likely be _worse_ at picking colors
which (to the average eye) goes together well. Maybe she just have good taste?

~~~
kaitai
How do you justify the idea she'd be worse at picking colors that go together?

If you pick points that are close together in four-dimensional space (to make
a simplistic analogy) they'll continue to be "close" in a topological sense
under any linear projection to three-dimensional space. Or for a different
analogy, if objects group together under a filtration, they'll continue to
group together under a coarsening of that filtration.

~~~
goto11
"Go well together" is different than "close together" if we are talking about
matching clothes. Color matching effects is based on distances in the color
wheel. Closest together is boring, largest distance is jarring. If you imaging
a new axis only visible to tetrachomats, the color matching effects
appreciated to a tetrachomat will most likely not have the same effect or even
be visible to regulars.

------
OscarCunningham
Are Antico's colourful paintings really a result of her tetrachromacy, rather
than artistic flair? If she's painting such that the colours of the paint
match what she sees, then trichromats should also think the paints match what
they see, since they're less discriminating than she is.

~~~
TheOtherHobbes
Distorting colour is a standard post-Impressionist painterly technique.

But the moonlight painting gives it away. Most people don't see _any_ colours
under low light, and being able to see and paint a colourful scene under those
conditions is a unique ability.

Of course it could be imagination, but it doesn't look like it. The tree and
the moonlight paintings have similar colours to the ones you'd see if you took
a photo of a scene and turned up the saturation in Photoshop, with a few extra
shades. It's a surprisingly literal and unimaginative form of exaggeration,
and it's not how most painters distort colour for effect. So I'm more inclined
to think it's a perceptual feature, not a creative choice.

------
crazygringo
I find tetrachromaticity fascinating -- particularly, I wish there were a way
to scientifically prove whether tetrachromatics actually perceive colors as
_qualia_ that the rest of us don't, because that is absolutely _not_ clear.

Let me explain: our eyes perceive RGB, but we don't in consciousness -- the
RGB is mapped somewhere, long before consciousness, further in the brain to
more of a perceptual RYGB -- a two-dimensional space of warm/cold (RY/GB)
against "lighter/darker" for lack of a better term (YG/RB). See [1] for more
info. Psychologically yellow functions as a primary color even though we don't
have a rod for it. (In reality it's much more complicated than this, since we
perceive saturation, brightness, etc. but this is a valid simplification for
current purposes.)

So it's entirely possible that tetrachromats map their four rods to the _same_
RYGB box the rest of us perceive as qualia, only with a different mapping.
Then, they can still distinguish between colors everyone else sees as the same
(because different spectra), but they'll still _perceive_ them as the same
color qualia the rest of us _perceive_ \-- colors in the world will just be
mapped slightly differently. The closest (but imperfect) analogy I can think
of is wearing polarized glasses -- same color gamut, but certain things
"compare" differently now.

Or, does tetrachromacy somehow also change the perceived-qualia RYGB model
itself? So there's, say, a 3rd axis beyond warm/cold and "lighter/darker"? Or
the span of the two axes somehow becomes wider to accomodate more information?
Or something else?

Hope this is clear. Perhaps it could be tested psychologically, though --
simply by asking participants to describe the colors they see qualitatively,
to see if the words they use in color comparisons (e.g. warmer/colder) are the
same as those used by the rest of us... or if there's any new "feeling"
component involved.

[1]
[https://en.wikipedia.org/wiki/Opponent_process](https://en.wikipedia.org/wiki/Opponent_process)
\- "...the cells were widely called opponent colour cells, Red-Green and
Yellow-Blue. Over the next three decades, spectrally opposed cells continued
to be reported in primate retina and LGN."

~~~
EventH-
Not sure what the justification is for saying Y functions 'psychologically' as
a primary color. It would be a secondary color (R + G) in terms of the light
spectrum, and (as you noted) our cones are directly most sensitive to RGB.

To answer the question, as qualia cannot be compared from person to person,
there is in principle no way to show that they differ (or are the same)
objectively. A sort of relative comparison of qualia within an individual (as
you propose) will also not get you there, as it may be that the individual is
simply more sensitive to changes along the gradient, not that they are
experiencing a new color, and that's assuming we are able to use an objective
comparison scale which we aren't.

~~~
OscarCunningham
> our cones are directly most sensitive to RGB.

The L cone is actually most sensitive to the yellow wavelengths.

~~~
EventH-
You're right, thanks.

------
peter303
I saw a six color channel video system at SIGGRAPH some years ago in their
emerging technology exhibition. I believe the developer may have been Sony,
but could not find an online reference. The additional colors were
approximately midway the R-B-G colors conventional used. They claim they could
display more of the color that people normally are sensitive to. And they had
a 6-color monitor side-by-side with conventional showing how nature scenes
were more vivid in their system. Of course every part of the system had to
double up: video camera, transmission, storage, display.

I do not know if subsequent technologies like OLED, Quantum dots, HDF capture
much of the color increase of the six channel system.

I do not know if the six color system could be used to quantify tetrachromacy.

~~~
WrtCdEvrydy
Quattron TVs tried this with a dedicated yellow pixel and weren't that good...
I highly doubt we'll see something beyond RGB (unless it's a first class
citizen from camera to TV)

------
goto11
I wonder how such people experience pictures, movies etc.? All color
reproducing technology is based on the the three-color system.

I'm skeptical of the articles claim that the painting gives us any insight in
how a tetrachromat perceive the world. This is just like claiming a color
blind person would be able to perceive full-color vision by looking at a
painting. Never mind that tetrachromat painters would have real difficulty
finding the necessary color pigments to reproduce what they see.

~~~
OscarCunningham
>I wonder how such people experience pictures, movies etc.? All color
reproducing technology is based on the the three-color system.

Presumably like trichromats experience Kinemacolor
([https://en.wikipedia.org/wiki/Kinemacolor](https://en.wikipedia.org/wiki/Kinemacolor)).

------
gatherhunterer
The title is misleading. The extra cone allows tetrachromats to appreciate
individual colors that the normal optic system would “average” into a single
hue. The visible spectrum is the same for tetrachromats: they cannot see
infrared or ultraviolet wavelengths. These individuals see more color detail,
not more colors.

~~~
masklinn
> These individuals see more color detail, not more colors.

If you're not able to differentiate between colors you're not able to _see_
those colors.

Hell, your argument can be stretched to stating that there's no difference
between monochromatic and trichromatic vision as long as the covered light
spectrum is the same.

~~~
gatherhunterer
You misunderstand. Any trichromat could see those colors as well, they would
just need to be much closer to the object in order to distinguish them. You
are still thinking about them seeing more colors. They see more detail in
color. Detail is not a matter of visibility but one of perspective. With a
closer perspective you could see those colors as well.

~~~
OscarCunningham
I don't think that's true. Deuteranopic dichromats can't distinguish red and
green by looking more closely.

~~~
gatherhunterer
Dichromatism is a disorder. Our brains expect a trichromatic signal and when
it only receives dichromatic information the hues are “repeated” because a
cone (usually the one responsible for green) is not available. In people with
green-weak color blindness this makes green look like a “weak” reddish hue.
Tetrachromats’ brains are still expecting a trichromatic signal but they get
more information than is expected. That means that the image contains more
information or detail but the colors are not nee colors.

~~~
masklinn
That’s not how brains or vision work. The brain is not “hard-coded” for
trichromatism. Were that the case we would not be trichromats in the first
place.

~~~
HeWhoLurksLate
Our brains are rather complicated, interesting things- and probably do
something like wire themselves up to whatever "sensors" are available.

------
Aardwolf
I'd love to see a tetrachromat who also knows about scientific color theory
(tristimulus curves, CIE XYZ color, chromaticity and whitepoints, ...) explain
how the color science would looks for them (do they have 2-dimensional hue,
and 3-dimensional chromaticity diagram?)

------
tzs
I wonder if commonly available color changing smart bulbs, such as Philips Hue
bulbs, have fine enough color control to be able to produce color changes that
only a tetrachromat can see?

If so, that would be an interesting way for a tetrachomatic magician with a
mentalism act to have their assistant pass them information. In particular, it
would almost certainly work to fool Penn & Teller on their show "Fool Us" [1],
where it often comes down to whether or not the mentalist can find a way to
pass information that Penn & Teller can't spot.

[1]
[https://en.wikipedia.org/wiki/Penn_%26_Teller:_Fool_Us](https://en.wikipedia.org/wiki/Penn_%26_Teller:_Fool_Us)

~~~
BurningFrog
I'd be really surprised if the Hue internally doesn't just have three lights
(R, G & B) that combines to produce all colors a human "trichromat" can
distinguish.

To my mild surprise, 10 minutes googling did not find any description of how
it works.

------
Waterluvian
Does finding advantageous mutations like this give us a sort of blueprint if
one day we wanted to artifically modify genes for these traits?

~~~
Merrill
Adding genes for more opsins is interesting. However, the regulatory
mechanisms for developing the retina and differentiating cone types appear to
be quite complex.

------
eeZah7Ux
12% of women is not exactly "rare"! The fact that it did not come out before
is telling.

It's interesting to notice how designing screens to use the RGB colors is very
limiting for those people.

Imagine living in a world where 94% of people have the same form of color
blindness and you don't.

People would randomly mix e.g. blue and green in every place and ignore your
comments with a smirk.

~~~
zozbot234
12% per cent of women is roughly 6% overall, that's quite rare. 94% of the
population can't perceive this.

~~~
fwip
I don't think 1 in 16 is "quite rare." If you've got 100 people you know by
name (and you likely have more), 6 of them have got this.

~~~
LocalH
_May_ have this. Odds don't necessarily imply even distribution amongst a
given sub-population. A person could know 1,000 people and still not know a
single tetrachromat, and another person could know 10 people and know multiple
tetrachromats.

~~~
fwip
No, 100 of 100 "may" have this.

------
k_sze
Is it possible that tetrachromat people may have a lot of trouble shopping for
painting supplies? Since the dye or pigment used on the packaging may not be
the same as the dye or pigment in the actual pastel/watercolour/whatever.

Wouldn't it be really confusing?

Are there lines of painting and art supplies specifically for tetrachromats?

------
officemonkey
There is always a relevant XKCD. In this case, I've had this blog post
rattling around my head for over 9 years.

[https://blog.xkcd.com/2010/05/03/color-survey-
results/](https://blog.xkcd.com/2010/05/03/color-survey-results/)

------
gameguy43
Super interesting. My notes as a colorblind man (might be misunderstanding
some stuff though):

(Being a little sloppy with sex stuff here. Not all women have two x’s, women
can be colorblind too, etc.)

• Two of our usually-three cones are specified on the X chromosome

• When one of a woman’s X’s specifies an anomalous cone she ends up with a
4th, anomalous type of cone.

• This happens ~14% of the time for women.

• That’s about the same percent as color blindness in men.

• That’s not a coincidence. Because color blindness comes from one of these
women’s sons getting that anomalous 4th come instead of a typical 3rd cone.
This anomalous cone tends to overlap more with one of the other cones in its
range of perceived frequencies, which is what causes color blindness.

• But only a small percentage (not sure what percent yet?) of these women with
4 different cones actually seem to be able to perceive more colors

• that’s because the 4th, anomalous cone might basically fully overlap with
one of the typical ones in its perceived frequency range, so it doesn’t really
give the brain any additional info

• one question I have: so it seems like not all these anomalous cones are the
same. Is there a fixed number of types? Or is it more of a spectrum? Further,
are /all/ cones on a variable spectrum? Or is almost everyone’s blue cone
exactly the same?

• this was interesting: colorblind men actually have a set of colors they can
distinguish that people with normal color vision can’t (the article explains
why)

• in this study they found colorblind men (but by looking at unusual things
they /could/ see, not things they couldn’t? Not sure) and then tested their
mothers to see if they could see extra colors.

• Most of them couldn’t. One of them could. The study was only like 9 people?
Safe to say /all/ of these women had 4 types of cones, even though only one of
them had a sufficiently non-overlapping fourth one to get some benefit?

• As a colorblind man, I’ve never noticed an ability to distinguish colors
others can’t. Only the opposite.

• it’s intellectually neat to know that’s possible, even if it doesn’t tend to
“come up” in everyday life.

• It souuuunnndssss like the amount of extra color vision that these
tetrachromats get is only the same as the extra color vision /I/ get—that same
“theoretically there, but doesn’t seem to come up in everyday life” thing.
That’s a little disappointing—I though tetrachromacy was more kooky.

~~~
3pt14159
> Or is almost everyone’s blue cone exactly the same?

I get a stronger blue channel from one eye than the other. So I'm quite sure
that there is variability, it's a matter of degree. Also, research into
language and culture shows that the brain is heavily influenced by colour as
well. Some cultures have difficulty seeing differing shades of blue or green
that westerners think are trivial.

------
pilooch
What would be a good source of tetrachromat images ? Would love to train a
model and "see" what these women see !

~~~
OscarCunningham
[https://www.dpreview.com/articles/1471104084/sonyrgbeccd](https://www.dpreview.com/articles/1471104084/sonyrgbeccd)

Alternatively take photos with a normal camera and then with the same camera
with a coloured filter. Choose the filter so that it only partially interferes
with each colour of sensor (magenta should work well). Then the two images
have _six_ independent colour channels between them.

------
zeristor
At what point would it be worth accommodating to these tetrachromats?

Sensors, displays, software.

Unicode encompasses vast numbers of characters, wouldn’t an update to colour
science and displays be in order?

~~~
mike_hock
When they're well into the double-digit percentage of the population, I guess.
(Not just _technically_ tetrachromats but actually able to discern a
4-dimensional color space).

Since they can perceive _more_ colors, it's never an accessibility issue, so
it's far more important to accommodate dichromats, and that's already very
hard because we can't tell how a person with a different set of cones would
perceive a particular color just by looking at it.

Also, we already have a color model that can't reproduce true cyan as
perceived by "regular" trichromats, and so far that hasn't been a real issue.

~~~
raxxorrax
What is the problem with cyan? That there is no adequate color space that can
create more or less cyan? I would think it is just a mix of green and blue,
no?

Is the same true for magenta as well? Is it a problem to convert between RGB
and CMYK?

~~~
OscarCunningham
RGB only spans a triangle within the full colour space
[https://en.wikipedia.org/wiki/Wide-
gamut_RGB_color_space#/me...](https://en.wikipedia.org/wiki/Wide-
gamut_RGB_color_space#/media/File:CIExy1931_AdobeWGRGB.png). So the cyan
generated by blue and green isn't as saturated as it could be.

~~~
mncharity
For anyone puzzled by the graphic's D50 whitepoint marker being in yellow,
offset from the color background's whitepoint (the white intersection of the 3
"arms"), yeah, that's wrong. There's historically been a lot of broken
chromaticity code out there, and associated flawed diagrams.

------
exabrial
One on my buddies wives can see ultraviolet. It's sort of incredible, she
describes it as a very dark blue to white with brighter sources

------
mirimir
I vaguely recall an SF short story about a genetic or nanotech hack for
becoming a tetrochromat. Either by Greg Egan or Hannu Rajaniemi.

------
DanielleMolloy
Is there a reliable online test for tetrachromacy?

~~~
masklinn
Probably not: colors are pretty much always expressed in terms of RGB (at the
"standard" trichromatic peaks"), and displays work in those terms. So you
couldn't _express_ the colors in questions, nor could you have the display
show them.

~~~
guenthert
Outside the on-line/web sphere, there are quite a few other ways to express
(or specify) colours, but alas, they all seem to have been made by and for
trichromats ;-}

------
aloknnikhil
I have always found describing color shades interesting/mind-fuck. Does the
"red" that you see "red" to me? I am red-green color blind and a lot of "red"
looks "brown" to me.

~~~
xwdv
Color doesn’t actually exist. We don’t see actual objects as they are, we see
the light that bounces off of them. Brains will create their own way of
mapping wavelengths to colors, so therefore we do not see the same thing, but
we perceive it as the same.

If I opened your brain and swapped your red with blue, you would not notice.

~~~
gatherhunterer
Color does exist. The wavelength of light that is reflected by an object is
its color. That wavelength can be measured objectively.

~~~
BurningFrog
Yeah, but all real light is a mixture of a _lot_ of wavelengths that our
retinas filter down to three aggregates of "red", "blue", and "green".

------
dr_dshiv
Birds have 4 primary colours and six secondary colors...

------
mirimir
Personally, I'd rather see further into the IR.

------
jakub_g
Summary: About 12% women have a mutation due to which they have 4 cones
instead of 3 in their pupils. Most of the time the extra cone has an
activation curve so close to another existing cone that it makes no practical
difference.

But in rare cases extra cone has a quite unique activation curve and allows to
differentiate mixes of wavelengths that are perceived as the same color by
most people.

More in-depth explanations: [https://theneurosphere.com/2015/12/17/the-
mystery-of-tetrach...](https://theneurosphere.com/2015/12/17/the-mystery-of-
tetrachromacy-if-12-of-women-have-four-cone-types-in-their-eyes-why-do-so-few-
of-them-actually-see-more-colours/)

~~~
layoutIfNeeded
In their pupils?

~~~
willis936
Rods and cones are in the retina, which is the inner lining in the back of the
eye. You see the retina when looking into pupils.

------
kingkawn
If men were the ones who had this the tenor of dismissiveness sprinkled across
our comments would be transformed into the desperate attempt to convince that
we all had this

------
kebbekaise
100x is sensationalist phrasing. ~7 more bits of color resolution better way
to think about it.

~~~
yarg
I don't know where they get the bit count from, it seems to be based upon an
understanding of the cone's operation that I've never seen justified in any of
these articles.

Assuming that the cones of different frequency range have approximately the
same degree of sensitivity, I'd be thinking that the number is about n^(4/3)
where n is the number of colours perceivable by trichromats.

But even if that's true - which I doubt - the additional colours are in
unlikely to have a useful distribution, and will be centered around the
frequency response curve of the fourth cone (I believe it's generally in the
yellow spectrum; somewhere between red and green).

~~~
OscarCunningham
If you wanted to measure it in a principled way you could count how many
colours they could _distinguish_.
[https://en.wikipedia.org/wiki/MacAdam_ellipse](https://en.wikipedia.org/wiki/MacAdam_ellipse)

------
IshKebab
100x more colours is just nonsense. Trichromacy is already sufficient to see
_all the colours_. The only difference is that some things may look like they
are a different colour (which means they might be able to distinguish two
objects where tetrachromats can't).

------
petewailes
On a related note, when you see purple, your brain falls over, because it's
actually seeing something it thinks should be green, but knows it isn't.

[https://toughcompetent.com/blog/purple-doesnt-
exist/](https://toughcompetent.com/blog/purple-doesnt-exist/)

~~~
thaumasiotes
Not a promising opening:

> Whilst we can see violet and blue next to each other, there's no purple.
> Because purple doesn't exist.

Back in reality, "purple" and "violet" are synonymous.

The article also makes the completely unsupported assumption that the color
you "should" be seeing when you look at a mixture of wavelengths is the color
of the average wavelength of that mixture. That's how it decides that purple
"should be" green. But that's nonsense.

> When you see red and green for example, the L and M cones both fire, and
> your brain interprets the result as something near both. And what's near
> both is yellow. So even though there's no yellow light entering your eye,
> your brain imagines the result as yellow, because both cones are being
> stimulated in similar amounts.

This gets the causality backwards. When you see red and green, your L and M
cones both fire. And you interpret that as yellow, _because yellow is what you
perceive for that pattern of cone activation_. To the brain, cone activation
patterns are all there is. The question "what single wavelength would best
approximate this activation pattern" is not even part of the model the brain
is working with. But, obviously, if there is a single wavelength that
approximates the activation pattern of a mixture, you'll perceive those two
things as being similarly colored. Is it necessary for the single wavelength
to be the arithmetic average of the wavelengths in the mixture? No.

~~~
egypturnash
> "purple" and "violet" are synonymous

Except when they’re not. People who have to think and talk about color on a
regular basis, such as artists, sort colors into much more detail than people
who don’t.

Have a look at the Wikipedia pages for purple
([https://en.wikipedia.org/wiki/Purple](https://en.wikipedia.org/wiki/Purple))
and violet
([https://en.wikipedia.org/wiki/Violet_(color)](https://en.wikipedia.org/wiki/Violet_\(color\))).
The image examples given for purple range widely, from a photo of some grapes
I would call more blue than purple, to a dress that I would call magenta at
best. And a color swatch that is somewhere in the middle of that range.

Meanwhile the page for violet leads with a specific wavelength, and a set of
photos that are all very close to the swatch above them. This particular color
could fit into the range of colors given as examples of “purple”, towards the
bluish end of the range.

------
SEJeff
Maybe they're like the mantis shrimp, who can see 16x more spectrums of light
than we can.

[https://theoatmeal.com/comics/mantis_shrimp](https://theoatmeal.com/comics/mantis_shrimp)

