In every wood, in every spring
There is a different green
from “I Sit Beside the Fire” by JRR Tolkien
I’m always reminded of the above whenever anybody irritates me by saying “If you’ve seen one you’ve seen them all,” but today I’m reminded of it for a different reason.
Charley mentioned to me a while back that some cultures don’t differentiate between green and yellow, instead calling them different shades of the same colour. I realised that we do it in English too. Most of the time the only people differentiating between mauve and puce — both weird purplish colours — are paint companies. (Did anybody else know that all sorts of colour names have specific numerical definitions, at least according to wikipedia? Puce is #CC8899.) This begs the question, how many colours are there?
The first obvious problem is that you have to define what a colour is. Ask a web designer and they’ll say about 16 million, while a kindergartener might name a dozen. Someone who thinks they’re very clever might say there’s only three primary colours. I can’t help but suspect that the three fundamental colours are biological. We have three types of cones that detect light in our eyes, but some animals have 4 or 5, effectively giving them 4 or 5 primary colours. Birds, for example, have a cone which can see ultraviolet light.
Further complicating things is that there’s no way to see what colours another person is seeing. While two people may say a ball is red, the mental image one person assigns to that particular combination of light that makes “red” might actually be “green” to the other person. Somewhere in our brains there’s a translation between input from our retinas and a mental image of a colour, and there’s no reason to think everybody has the same translation, even though the English word attached might be the same.
Now this point about colour being arbitrary is often used as an example to support some idea that reality is subjective — I think that was Charley’s original point in bringing this up. However, colour is special in that there is no second sense to confirm what we see. Two people see a ball, and since both can touch it and confirm it’s there, they know that they both see the same ball, but there’s no way to compare mental pictures.
The strangest artefact of this conversion of wavelengths or energies into a mental image is the twisting of a linear scale into a circular one. Why should the end of the spectrum wrap back onto the other end? Red goes to orange goes to yellow goes to green goes to blue goes to purple goes to red. This I can’t find a biological explanation for, but if anybody knows I’d like to hear.
Granted, the underlying physics of light is quantum so there is a specific number of energies of light that a person’s eye can see, but human perception muddies it all up. Trying to understand the resultant continuous perception in a discrete kind of way doesn’t seem informative to me, as convenient as it might be. The problem of discretizing continuous variables plagues psychology, philosophy, and all the social sciences. I think we’d get a lot more from these disciplines if we made a habit of conceptualizing them in continuous terms.