how do we know if we perceive colours the same way?
In: 19
Your question is actually kind of fuzzy — ignoring the “how” it ranges from “easy yes” to “complex mostly/maybe” to “easy no” — so I’ll briefly introduce some concepts and then re-ask (and answer) three different versions of your question.
In psychology, neuroscience, and cognitive sci they distinguish *sensation* and *perception*. In the case of color vision, *sensation* would the different wavelengths of light from the world stimulating different receptors in your eye (for a non-colorblind human, light will stimulate red, green, and blue receptors with different intensity to make up the visual spectrum), and then signalling the brain. Most types of [colorblindness](https://en.wikipedia.org/wiki/Color_blindness) would be due to a problem in these receptors — a problem of sensation. *Perception* in vision is the processing of the signal in the brain into information that we then have both subconscious and conscious response to. There are [several types of blindness, colorblindness, and other vision disorders that can originate at any stage of processing](https://www.scientificamerican.com/article/when-blindness-is-in-the-mind/) in the brain — a problem of perception.
For science and medicine, the definition of *perception* is bound by what an independent researcher can observe or measure in a subject. Measuring at one end (again, in color vision) might involve examining both what you say you see and how your body reacts to viewing something like the bubbly circles in the [Ishihara colorblindness test](https://en.wikipedia.org/wiki/Ishihara_test), while on another end it might involve an interview asking you to describe what the color green “looks like” and “feels like”. What is interesting it that even though the latter is a subjective test, there tends to be some interesting consistency within a culture, and even worldwide — take color theory in European Art, for example, in particular the concept of [warm vs cool colors](https://artincontext.org/warm-colors/) which is completely subjective, synthesizing emotional memories and the perceptions of two different senses (color via vision and temperature via touch), yet somehow for any age group in students’ first ever art class they agree remarkably well on what’s warm (reds) vs cool (blues). Examples like these and associated experiments all provide a general picture that as far as measurable *perception* is concerned, healthy people in the same general culture have the same general perception of colors.
So a scientific understanding of someone’s perception is limited to what’s so far measurable by an outsider. But all the words and emotions I can spill on paper won’t describe what makes the color red look so brilliantly “red” — what “redness” is — these are called [qualia](https://en.wikipedia.org/wiki/Qualia) in philosophy. There does not seem to be any way for one person to get any indication of the experience of qualia of another person, and it’s possible that the definition of qualia itself (as it is now) requires that it be unknowable to the outside observer (which may preclude it from being a useful topic of conversation by any means). [Mary’s Room](https://en.wikipedia.org/wiki/Knowledge_argument) is the thought experiment used to illustrate all this — whether a neuro/optical scientist whose entire life from birth has been in an environment without a single red-colored or red-reflecting object would, upon suddenly seeing the color red for the first time ever, gain new knowledge.
So the question for you, OP, is *which question were you actually asking*? Do we (as in, generally healthy non-colorblind humans) have the same *sensation* of color (yes)? Do we have the same *perception* of color (most stuff I’ve seen (I’m not in this field) indicates again yes, but it’s much harder to measure generally)? Do we have the same experience of color *qualia* (there is literally no way to know… unless you have some ideas…)?
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