Etydhv

I've heard it said that white light contains all the colors in it. Our sun produces white light and that the visible spectrum is just the range we evolved to see because our atmosphere is transparent to it.

Every planet with an atmosphere in orbit around a star will have it's own visible spectrum for the life evolving on it's surface, potentially causing those lifeforms to have their own concept of "white" which may be the color their star emits, or maybe the collection of all colors in their visible spectrum. In other words, they may call red (Or whatever color their star is) white and say it is the collection of all colors.

Some other planets may even have atmospheres where the visible spectrum is too dark, or doesn't reflect off of common materials in a way that is useful for eyesight. On such planets, vision may not even be a trait that evolves in the first place.

My question is: how special is our situation? How many outcomes are there to the life-atmosphere-starlight equation and how likely is each to occur?

Probably not. But they will likely see white.

First, White is just a word it has no intrinsic meaning.

Second white to a human may not be white to a bird or lizard. Our colors or lack there off is an artifact of how we see light, which wavelength sensitivities we have.

Will light from their sun look white, probably. Not for any intrinsic reason but because of evolution. Eyes tend to evolve for the spectrum of light available. If they have color vision it will likely see naked sunlight as the default (white) since color is based on differential absorption of the light from that source. Whatever "color" the light that reaches the surface that is what they will see as white. The only way they would not is if they orbit a dual star system, in which case they will see the average light that reaches the surface as white.

OUr sun will not look white unless their star is very similar in color.

Obviously, you don't literally mean "will they use the phonemes we put into the English word 'white' to describe the color they see?"

Because not even terrestrial humans do that, apart from some of the minority who speak English.

So I'm guessing you mean "will an alien that can see color always come to consider the light that they get from their sun to be a 'neutral' color?"

It depends. Obviously, if their atmosphere filters a lot of the light, then their eyes will not be adapted to the light of the sun above the atmosphere, but tot he filtered light.

If there's a brighter or more constant light source than the sun, then their eyes will be adapted to that.

An aside about vision.

Most of us see colors in basically the same way: we have three receptors for reddish (low frequency, long wavelength), greenish, and blueish (high frequency, short wavelength) in our eyes. The color we see is caused by a mix of those colors.

So if we see a color between red and green, we see yellow.

If we see a color between yellow and blue, we see cyan.

And if we see a color between red and blue... well, that's the color inbetween, so we'd see green. But if we see TWO colors, red and blue, mixed, then we see magenta. Magenta has no wavelength. It's not a "real" color at all.

Not everyone sees color this way. There exist people with more than three types of receptor: tetrachromats. There exist colorblind people, with fewer. Unless they have no color receptors at all, they have their own "magenta"s, made of no real color.

There's a whole bunch of light from the sun in the UV and IR ranges, which we do not see, and which do not make up part of our definition of "white".

So it is arguably false to say we call sunlight white. What we call "white" is a very small subset of the Sun's electromagnetic radiation.

And at sunrise and sunset, we might call the light from the sun "red" or "orange".

We are also more sensitive to some colors (red) than others (blue). So it takes less of them put together to make up what we'd call "pure white" where our color (but not brightness) receptors are flooded.

So would an alien know the colors they could percieve, as "white"? Well.... yeees.

As others have said, it's a slippery word.

Look through night vision goggles:

That car is clearly "white". But it's clearly also "green".

So what we ourselves mean by "white" is complicated. We mean something more like "reflecting all the incident visible light in the current scene, but not coherently like a mirror".

It's likely that any alien capable of seeing color will be able to express a similar concept, even if their color perception is different to ours.

After all, colorblind people do, and so do tetrachromats.

And, if the wavelengths they consider "visible" are significantly different to ours, something they describe as white we might call black (some black t-shirts glow white in IR, for instance).

The wavelengths they consider visible are likely to be some subset of the wavelengths available to them.

So would they call our sun "white"?

Eh. If they're from a red dwarf, probably not. They would likely consider it "yellowy", if they had the concept of "yellow". "Averaging a little more in the short-wavelength part of the spectrum compared to what we'd call white", they'd say.

I follow your logic. Generally. I would agree. The main problem is the hand waving we need to do to talk about perception. Some would argue about whether or not we all see the same "red". I don't think those arguments are interesting or useful as they're not falsifiable.

Now here's some hair splitting idea: Consider the Mantis Shrimp and its 12 types of photo receptors and solar spectrum gaps. I could imagine an organism evolving a system if vision detailed enough to see the variations in the spectra between stars. Then it would be able to tell the different between true white-full-spectrum light and the light from the sun.