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Comment by SAI_Peregrinus | Hacker News Reader

It also needs a bit of biology. Our eyes don't have a flat response over frequency, they're more sensitive to blue than violet. Violet gets scattered even more than blue, and the violet light does shift our perception of the color. But it does so less than it would if we had photoreceptors more sensitive to violet, so the resulting perceptual color depends not just on the intensity of the light at different frequencies but also on our particular biology. People with tritanopia (blue-yellow color blindness) don't have blue-sensitive cones (S cones) and thus to them there is no perceived blue. Not to mention the linguistic history of the word "blue" and why English uses "blue" instead of "青" or some other word, the questions around qualia & what it means to perceive color, etc.

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There are differences in receptor behavior across species, but they are understandably clustered around the parts of the spectrum in which sol is most luminous. An earth-like planet orbiting a different star would likely have evolved photoreceptor arrangements which match that star instead. So after scratching the biology itch we'll probably need to talk about fusion byproducts in sol-like stars.

> they are understandably clustered around the parts of the spectrum in which sol [sun] is most luminous

That would be understandable but it’s not what’s going on: http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.h...

I didn't know that about water, thanks.

Ah - so I guess that's why snakes have pit sensors for infrared.

> An earth-like planet orbiting a different star would likely have evolved photoreceptor arrangements which match that star instead.

No, not really- the limitation is chemical, not evolutionarily-driven. Earth is very well lit in infrared, but it's very difficult to make a chemical that is biologically useful for seeing infrared because the wavelengths are just too long. Its very challenging to do more than the most primitive kinds of sensing in infrared. If our sun was much dimmer, we would probably be blind, but if not our eyes would still not see in far infrared. Same goes for ultraviolet- the energy is too high and molecular bonds are too weak. Seeing in visible light is a reversible reaction, but ultraviolet wouldn't be.

What you're saying is true of ocean animals, especially in the deep sea. They don't see red very well or at all, but the evolutionary pressure against seeing red is not terribly high except very deep where food is very limited.

There also is evolutionary pressure on our vision, but it has nothing to do with the sun. We're twice as sensitive to green since it is so common and important, but green comes from photosynthesis and not from the color of the sun. In a way, we are most sensitive to the least important color of light- the color that is not absorbed by plants. The wasted, useless byproduct of sunlight is what lets us identify food.

Plus, we actually basically only see in blue and green. The overlap between rods and red/green cones is huge. "red" and "green" as we perceive them are mostly fabrications of our neural circuits- if we were seeing them how our photoreceptors actually receive light, all shades of green/red would be very strongly mixed together. All shades of red would look significantly green except for the very farthest reds, which would look very dark because of low sensitivity.

dogs see violet better, so "normally" our sky would be blue to them. But because their eyes have only two types of color receptor, they see violet as blue, and our sky is also blue to them.

Same outcome, but for a different reason!

The real question is, is the sky blue for everyone? Some creatures can see ultraviolet. Some lack color at all…

Some animals have more cone types than humans, especially various birds, so would probably see a violet sky.

We don't have this because common ancestor for all mammals lost all cones but one, perhaps due to being nocturnal, and a second was re-evolved as mammals became more dominant (after dinosaur extension). A third cone was evolved in primates due to a gene duplication that gave us our green cone

https://www.sciencedirect.com/science/article/pii/S004269890...

maybe in 100M years we'll get a 4th cone or rod. Probably from nuclear mutation...

We already have mutations, generally in women, for tetrachromaticism, who usually have male relatives with severe or moderate color blindness, in which the X chromosome encodes a different green cone. So they end up seeing red, strange-green, green, and blue, where strange-green is somewhere closer to red than green.

Only a few on record but they tend to have absolutely insane color matching and color perception. One of note worked in the fashion industry and could match fabrics perfectly even in varying lighting (e.g. working under fluorescent but able to match colors that would stay matched in halogen/stage lighting)

I have that already ;) it actually looks like muddy puke green than green. However, green stop lights look more “white” than green.

Some reds look like brown. I hate reds. I’m not sure about the Pantone-like color matching but I definitely see different colors than most people. To the point where my flight license is restricted.

Dichromatic but not trichromatic.

Not sure if you'll see this but you should check color perception with any female relatives, they're much more likely than average to be tetrachromats!

how does dichromatism restricts flight license? no instrumental flights? no night flights? something about perceiving warning lights on some panels?

All three

There's some evidence that tetrachromacy already exists in a few humans. If so we have the gene already. But why would it spread?

fringe theory just for a bit of fun: since screen use 3 colors diodes, maybe people with tetrachromacy would be less addicted to screens, making them both more grounded in real life and marginally more successful, leading to them having more children?

I have no idea how to test it. But in my heart I know that screens with RG, GB or RB color models would suck enough that any screen addiction would be cured instantly.

I wouldn’t be so sure, for a decade all we had was G and we used more and more of it until we died of dysentery outside Eagle River.

You were supposed to ford the river!

You know our supplies were:

1 axle.

1 wheel.

1 bundle.

100 boxes of ammo.

10,000lbs of bear meat.

2lbs of squirrel meat.

We sank like a rock.

They need special screens with four colors and the internet updated to make it more interesting for the tetrachromatic.

this is true of many human mutations with the development of medical care, its not like we face evolutionary pressure for many things

> maybe in 100M years we'll get a 4th cone or rod. Probably from nuclear mutation...

There’s a Greg Egan short story (I think it’s ‘Seventh Sight’) where a bunch of formerly blind kids with cybernetic eyes hack the receptors to respond to wavelengths other than the traditional RGB. So perhaps it wont take millions of years.

I puttered on a color interactive where, to emphasize this distinction between world-spectra vs brain-color, you could swap in color deficiencies, a non-primate mammal ( dichromats), and a monochromat.

this is fascinating because I'm red/green color deficient yet I have no problem seeing most reds or greens. I feel there's a "spectrum" of color that we all see and each of us is slightly different. My shade of green may not be your shade of green. Yet, when I point out my shade of green - it matches your shade of green because of our eyes. Even though we may be perceiving entirely different colors.

Most colorblind people aren't dichromats, they're so-called anomalous trichromats. Basically, the genes coding opsins in your eyes have a number of functional sites that tune the spectral sensitivity. Those sites are tuned as far apart as they can be in color-normal humans. Anomalous trichromats usually have a genetic error that causes their opsins' sensitivity curves to overlap more, which manifests as reduced color sensitivity.

This occurs in other animals as well.

Imagine a chromaticity diagram, but on a perceptual color space where long-range euclidean distance at least attempts to describe the magnitude of perceived difference (rather than the usual model artifacts) - so round-ish. Then decreasing perceived difference between red and green shows up as a smush to oval.

How would Lieutenant Geordi La Forge from ST Next Generations see the sky with his visor?

You know that scene with the Nexus ribbon? Probably a huge version of that. But it depends on what timeframe we’re talking. Visor Geordi or Eye Optics Geordi?

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