Following up on your comment, it can be more-or-less proved that human color is a neural construction based on light input by looking at things like optical illusions, such as this classic white-lines-and-black-boxes affair: http://www.michaelbach.de/ot/lum_herGrid/index.html
You might think this isn't a color demonstration, but it is actually a compelling example that beyond just the spectrum of the photons hitting your eye, the brain is doing a lot of additional work involving what we call "colors". Further evidence: The broad similarities between what attributes cultures ascribe to colors. Yes, there are differences too, but there's a lot of correlations there, added by your brain, which comes preprogrammed with some meaning-ish things. (It's not that direct, but since I'm working in English here that sentence will have to do.) We know we share similar "red" and "green" experiences because we share their clashing effect. I'm not sure if there's anybody who has ever moved from not-red-green-colorblind to red-green-colorblind, but in a real sense, a red-green colorblind person is seeing a different color, with different properties and different aesthetics. Their aesthetics aren't wrong, just different.
(Related: It is frequently complained that aliens on TV are just humans with a bit of latex stuck to them, but there are numerous other ways in which aliens are just "humans with bits stuck on", and one of the most notable is how many alien civilizations basically look good on TV. I'm willing to buy that an alien race building a real engineering artifact will build something with a form that appeals to us, just as many aliens-on-earth do (spiders, for instance), but their colors ought to be alternatively garish beyond belief, subdued beyond our ability to recognize (10 million shades of blue and combinations of blue), or just plain random (a gamut twice ours, perhaps, or a race with no equivalent to vision at all, though I find that one hard to swallow), as they work with colors that may happen to share the same wavelengths of light (or not) but otherwise have nothing in common with human colors.)
In other interesting thoughts, when we can directly stimulate the human optic nerve, I look forward to the seeing what happens when we move out of the CIE color space. IIRC, the boundaries of the CIE color space represent the point where the three color receptors in the eye would need a negative photon to generate that result, which can't exist in real life. This implies to me that such values could be generated by direct stimulation, though. Are there colors that no human has ever seen, but nearly every human is equipped to experience in much the same way as any other color, in some sense as much a color as any of the ones we know? Perhaps some of us will even find out, some day.
You might think this isn't a color demonstration, but it is actually a compelling example that beyond just the spectrum of the photons hitting your eye, the brain is doing a lot of additional work involving what we call "colors". Further evidence: The broad similarities between what attributes cultures ascribe to colors. Yes, there are differences too, but there's a lot of correlations there, added by your brain, which comes preprogrammed with some meaning-ish things. (It's not that direct, but since I'm working in English here that sentence will have to do.) We know we share similar "red" and "green" experiences because we share their clashing effect. I'm not sure if there's anybody who has ever moved from not-red-green-colorblind to red-green-colorblind, but in a real sense, a red-green colorblind person is seeing a different color, with different properties and different aesthetics. Their aesthetics aren't wrong, just different.
(Related: It is frequently complained that aliens on TV are just humans with a bit of latex stuck to them, but there are numerous other ways in which aliens are just "humans with bits stuck on", and one of the most notable is how many alien civilizations basically look good on TV. I'm willing to buy that an alien race building a real engineering artifact will build something with a form that appeals to us, just as many aliens-on-earth do (spiders, for instance), but their colors ought to be alternatively garish beyond belief, subdued beyond our ability to recognize (10 million shades of blue and combinations of blue), or just plain random (a gamut twice ours, perhaps, or a race with no equivalent to vision at all, though I find that one hard to swallow), as they work with colors that may happen to share the same wavelengths of light (or not) but otherwise have nothing in common with human colors.)
In other interesting thoughts, when we can directly stimulate the human optic nerve, I look forward to the seeing what happens when we move out of the CIE color space. IIRC, the boundaries of the CIE color space represent the point where the three color receptors in the eye would need a negative photon to generate that result, which can't exist in real life. This implies to me that such values could be generated by direct stimulation, though. Are there colors that no human has ever seen, but nearly every human is equipped to experience in much the same way as any other color, in some sense as much a color as any of the ones we know? Perhaps some of us will even find out, some day.