I think I've had this same conversation at least four or five separate times throughout my life, and I have no doubt that other curious people, very comfortable in the realm of questioning basic perception, have as well- do humans all perceive colors the same way?
That said, if you've never thought about this before- welcome to the mind of a scientific overthinker, this is going to start out as a wild ride and end in some cold hard facts that would have ended these discussions sooner had I known them the first time I asked myself this question.
It's the same basic idea that starts the conversation every time- what if we have all just agreed to call certain colors by name and we can all recognize them distinctly, but they all look different to each of us? For instance, we can all agree this apple is red:
But what is "red"? Is what I perceive and believe to be "red" also what you see, or do you see the color I perceive to be "blue", or "green"?
It's a pretty trippy idea- and one that in my experience, a lot of really cool and smart people explore independently at least once in their lives (if this is your first time thinking about this, I'm thrilled to be a part of your color relativity theorem journey!). So, I figured it was worth addressing here!
I appreciate the creativity of this idea- it removes the person asking the question from being at the center of the universe, and allows them to view themselves as more of a part of something bigger, which I think is pretty neat. So I think this is a good question to ask in terms of broadening one's view of the world and the way we understand ourselves and our role in the grand scheme of things.
That said- it's just not true. And believe me, I wanted it to be. I thought that would be so strange and so interesting to study, I had hoped someone found something to lead us to believe that color might be relative. However, both our biology and the physics of light lead us to believe that we do all, in fact, perceive color in similar ways.
First- WHY would that be helpful, from an evolutionary standpoint?
For a very long time, far back in the evolutionary history of the world, dinosaurs were the main animal life roaming the planet during the day. This made the night hours likely the best time for early mammals to do their hunting at a lowered risk of becoming a dinosaurs next meal.
That nocturnal behavior meant that rather than excellent vision, these animals likely had elevated hearing, and potentially a stronger sense of taste/smell that would help them navigate at night. However, in order for them to see SOME of the world around them, they also likely had bigger eyes, wider pupils, and more rod cells (more on that in a minute).
Clearly, a lot of mutation (which eventually gets called adaptation, when one mutation wins out over the others) occurred to get this system in place for early mammals to have a shot at seeing well in the dark. This night vision also equipped them with UV- and red-sensitivity, and it was later on in evolutionary history that mammals eventually gained the ability to see blue light as well (again, through a lot of mutations to our genome over time).
All that said- what evolutionary benefit would there be to all of us seeing colors differently? At no point would that have benefited humans as a species during all the time our eyes have been evolving and changing (and ideally making the world a place that is easier to understand through clear vision). Making each of us see colors in a unique way would add to confusion, especially when it comes to humans being able to communicate about colors and the way certain things look.
For example- if we were hunting and gathering, and I saw a very brightly colored red berry somewhere, tried to eat it, and it gave me a stomach ache, I might want to warn my friends not to eat that same berry. Let's say it made me so sick, I couldn't even remember the color- I just knew it was a bright color. If I tried to communicate not to eat the bright berries, excluding the detail that they are red (because remember, this shouldn't matter if we all see colors differently anyway), but someone else saw them as blue or green- those colors might not fit their idea of "bright", and they might make the same mistake I did and eat those berries.
See what I mean? From an evolutionary standpoint, it would make no sense for all of us to see colors completely differently from one another.
Second- Our eyes should all work the same way, and for the most part, they do.
Human eyes are fitted for daytime use, since we are most active during the day time and sleep at night. Our eyes are very intricate little devices, all with a similar set of parts- first, light hits our cornea, which is the bent front part of our eye that helps us bend and focus light (this is the part effected in people with astigmatisms). Next, some of the light will enter our pupil (the black center of the eye), and how much light gets in is controlled by our iris, which is the colored part of our eye. The light then passes through the lens, which is a clear inner part of the eye that works with the cornea to focus light, and then it finally hits our retina, which is a thin layer of cells that are receptive to the light and send signals about that light to our brains so we can interpret that light into images.
The two types of photoreceptors involved in capturing light are called cones and rods (if you look at the diagram below, you can see they got their names from their morphological shapes!). Rods work at very low levels of light- these were in abundance in the eyes of early mammals who hunted at night, since they are the primary contributors to effective night vision. Rods are great because they require very low light input to be active, however, they do not detect color, which is why nighttime vision usually appears in greyscale. Cones, on the other hand, require high light input, but allow us to see color! The three main types of cones humans have can detect red, green, and blue light.
All of this to say- our vision is a sophisticated, complex biological system. And if the natural world is anything, it's lazy! If something isn't broken, biology will not fix it. Having our cone cells detect different types of light (rather than blue/green/red, having some people see orange/blue/purple, for example) wouldn't help advance our species in anyway, and would probably involve a lot of changes to our eye morphology (or maybe even our nervous system and the way we transmit signals about light to the brain!).
Third- Light doesn't care about what you believe is red or blue, it's wavelength is the same!
So, we've established at this point that biologically, it makes sense for all of us to see color the same way. As a finale to this exploration of "color relativity theorem", I thought it was only appropriate to bring a little physics into our line of thinking.
Physics is cool because it applies to so many different components of life- magnetism, force, sound- but the one we'll focus on today is light. We've talked about how our perception of color is really dependent on light coming into the eye, bring properly focused, and then activating our cone cells which send a signal to our brain, which interprets what we see. However, it's not only up to those cone cells to determine the colors that we see- it's the light itself, activating those cone cells, that determines the color of the objects in front of us.
I want you to think for a moment to a time that you were deciding what to wear on a hot summer day. Most people learned at some point in their childhood (whether by sitting down on a black seat in a parked car, or wearing a black cap out to enjoy some time outside) that dark colors "absorb heat", so often when trying to stay cool during the summer, people opt to wear white. This heat absorption for dark colors (black, especially) is actually directly related to the way that we perceive the colors of those objects. Black and white are considered "shades" rather than colors in the art world- this is because black is the absence of color, and white is the combination of all colors. That is- black objects appear black because they absorb all colors of light. This means that no light reflects off of them, which makes these objects feel hot on a summers day. It also means there is no color light reflecting off the object into our eyes- therefore, we perceive that object to be black. Similarly, white objects reflect all the colors of light and absorb none- this attributes to these objects feeling cooler during the summer, and to our perception that they are white.
All the different colors of light have specific wavelengths, and our eyes can tell what color an object is based on what wavelength light that object reflects. This is perfectly exemplified by grow lights for plants- if you've never seen these before, they are usually a combination of red and blue blubs that help plants continue to grow even when there is not a lot of sunlight available (usually during the winter, when days get shorter).
These red and blue lights are used to encourage plant growth because both colors are absorbed by the plant- and, you might have guessed, we don't use green light because green light is reflected off the plant (which is why many plants appear green to us).
So, in order for us to see colors differently between people, we would need to perceive the same wavelengths of light as completely different colors, which isn't physically feasible with what we understand about light currently.
In conclusion
While it would be cool for all of us to see colors in a totally unique way, biology and physics can inform us that most likely isn't true.
However, that line of thinking, that questioning the things we take for granted as simple fact, is what keeps us pushing the frontiers of science, and the frontiers of knowledge and understanding! So even though this theory proves to be untrue- never stop asking those questions, and never stop looking for answers either.