I think thr op is actually exploring a deeper question. What if there were more degrees of freedom to our color perception? How would our brain deal with it?
Smell has many degrees of freedom. It just has no directionality. Well, in sharks it has one dimensional directionality, sideways, by comparing nostrils.
Picture something more like a spatial sense of smell. You would think of the scene you were looking at as being areas of different kinds of stuff and not areas of color or shade. Maybe like a map of a garden might have ten different sections for ten kinds of flowers.
If our spectrum was stretched so that deep IR was covered by our red perception, then how about this scenario:
Let’s say we have two blue mugs. One is full of hot coffee and hotter than the other mug which is empty. Would our brain, detecting this additional IR coming off the hot mug, mix in some red with the blue painted mug making it look purple?
If there was a third, cold mug but which was painted the exact shade of purple as the hot mug, would we not be able to tell which was the hot mug out of the two purple mugs without touching them to find out (or looking to see if any actually contained coffee!)?
I was wondering about this too. I didn’t know there was a thread on it. It seems odd that the 2 end colours, with the greatest wavelength difference possible, seem so similar. My best answer so far is that this is an artifact of using a finite number of colours to represent the spectrum.
Are there 6 colours of the rainbow ? or 7 ? or 8 ? Its all what you are taught.
If light green is separate to dark green, or not ?
We know why the brain perceives a single spectrum though.
The opposite ? Now look at a tv /computer screen that is filled with white.
Actually white is the sum of green red and blue dots, so we KNOW that the light coming from the screen is red, green and blue.
Well, if our colour receptors had purely unique ranges of vision, then we could, MIGHT, perceive that as three separate pictures.
A green picture,
A blue picture
and a red picture.
But no, because the receptors overlap, we’ve learnt to only ever see one image.
Why do I theorise this MIGHT ?
What if we had IR vision with non-overlapping receptor ? Then we might see a “heat” picture , separate to colour, because of how useful a heat picture would be to us.
This would be very similar to our aural ability to block out background noise, or listen to it.. we’d be able to ignore heat, or look at it, or both.. perhaps..maybe ..
still we’d have to learn it, and we may only learn what we are told to learn.
Perhaps we can see IR, so what if you tell kids that you can see heat ! They might learn to use their ability ???
In some ways there is not a lot of choice. They brain must work out how to cope with a signal that is red plus blue and no green. This isn’t a single spectral colour - so the combination must be a colour that isn’t actually created by a single wavelength. But the world is mostly filled with things that reflect more than a single wavelength, so it is useful. If, like most animals, we only had two colour sensor types we would see colours that would spread along a line. But because we have three, we have to resolve them into a triangle. One edge of the triangle maps to colours that can only be formed by a mix of red and blue, any colour in the interior of the triangle requires a mix of all three colours. Only the other two edges map to pure spectral colours. Thus you get your colour wheel, with one third of its edge made up of red through purple, magenta, violet and blue. Out perception of violet is probably partly due to a slight glitch in the red sensor’s response that responds just a bit to very blue light. This glitch breaks the pure colour wheel model slightly.
The issue is one of reflected light versus emitted light, and the wavelengths of those two. If you don’t mind shifting into the visible spectrum, you can actually do this exact experiment with hotter things using standard eyeballs.
Suppose you’ve got a room-temperature block of steel, and another block of steel that’s been heated to 800 C and is therefore emitting cherry-red light. You illuminate both of them with blue light. What do you see? My guess is that the apparent color of the hot block will be some mix of reflected blue light and emitted red light, and it will indeed appear purple.
I would guess that if we could see IR, a hot mug of coffee would have a color that is similarly a mix of emitted IR light and reflected ambient light (which may or may not include additional IR light).
Displaying a color spectrum as a wheel doesn’t have any physical relevance, since there’s a wavelength/frequency discontinuity between red and violet. However, the wheel (or triangle) concept is useful for visually explaining additive or subtractive color mixing, but only because there happen to be just three primary colors (corresponding to the three types of color receptors in your eye); that means we can have a two-dimensional color triangle and still be able to illustrate mixing between any conceivable combination of those primary colors. If there were four primary colors (R+G+B+IR), we’d need a color tetrahedron so we could illustrate mixing between any combination of those colors. If there were five (R+G+B+IR+UV) primary colors, we’d need a tesseract.
As for what IR and UV might look like if we could see them, that would depend on whether we have whole new color receptors for them (see previous paragraph), or whether our existing color receptors just developed broader ranges of sensitivity (i.e. your red receptors could see longer wavelength than they currently can, and your blue receptors could see shorter wavelengths than they currently can).
For broadband receptors, I suspect we’d just perceive more intense reds and violets in everyday life.
For eyes with new color receptors to cover IR/UV ranges, you could ask the mantis shrimp how things look; they have sixteen different types of color receptors in their eyes.
One could make a simple statement about perceived colour. If we retain our three receptors, anything we do to change the frequency range of our perception will result in colours that still look identical to what we perceive right now. We might shift around the frequencies, but what our brains “see” as any given colour will be one of the currently perceivable colours. As Machine Elf writes above, it is only if we add new receptor types that we perceive new colours - and that needs new brains to go with the new receptors. New brains means new everything, and no sensible answer to the OP.
yes, multispectral photography has been here since the days of film (although the false-colour films are pretty hard to get hold of now), look at the work of richard mosse - the aerochrome film he uses maps IR onto red
I don’t see any reason why there couldn’t be a wider range of perceived colours than we experience - brand new colours that we can’t imagine - in the same way, as Lemur866 points out, that a person with colour-impaired vision may not be able to imagine the full range of colours we consider normal.