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White is defined by the color of the sun. Since we evolved within its light we of course see the distribution of wavelengths that make it down to Earth's surface as white. Even if the sun was always orange, we would see that as white instead.
Do you have a source for that claim? There is no way we can validate that without sending humans to another solar system. And wait thousands of years.
Surely it is plausible that an organism that evolved vision under particular lighting conditions would develop vision adapated to those lighting conditions.
I'm not telling you it's not worthwhile to come up with ways to test the claim if you want to be rigorous (e.g. you could measure the wavelength sensitivities of the vision of nocturnal or underwater animals and see if there's a pattern). But to me it's pretty self-evident as a starting point at least.
Why do we see it as yellow, then?
Because our atmosphere causes "scattering" of hues in the highest frequencies. This is the same reason the sky appears blue.
Could also be redshift too. I don't know enough about it to know if we'd notice it over such a short distance and of a constant source, though. Definitely noticeable as reciprocity failure during long exposures in photography.
No, that's not at all what redshift is.
And neither redshift nor dopplershift would have that much effect on light at the speeds we're talking about.
Besides the sun's color on earth it's not a shift of wavelengths, it's a subtraction of wavelengths, as you easily can see in a spectrogram.
Do we experience Doppler shift with our own sun? I would assume as we are in a stable orbit we wouldnt
Strictly speaking since our orbit isn't a perfect circle we do move towards and away from the sun, so there will be some level of redshift. At those speeds there's really no chance of seeing it without specialised tools, in the same way you don't see redshift from a car driving past you.
Blue light gets scattered more by the atmosphere. So less blue light is received directly in a straight line from the sun and more is reflected from other parts of the sky. That's also why the sky looks blue in the day and why the evening sky looks red (if the sun is very low during the evening, the blue light can't reach you because it scattered so much due to the very long shallow way through the atmosphere)
During the day it's white, but it's also overhead and blindingly bright so we don't spend much time looking at it. As it gets closer to the horizon Rayleigh scattering begins filtering out the bluer light and the sun becomes yellow, then orange, then red. It also gets closer to our eyeline and becomes mildly safer to look at so we look at it a lot more. This in turn leads us to believe it's always yellow