Though vision as a whole is a complex affair, colou calculation is fairly straightforward, in that each type of cone can distinguish about 100 shades, so in total a million combinations are detectable to the human eye.
Whilst the average human can perceive a million different colours, in real terms, when considering visual ability, this fact is utterly unremarkable in every way. Though simple language can never truly capture the glory of the extraordinary range of colour shades we can see, many poets and authors have seen fit to try.
Human colour vision derives from cone cells in our eyes - there are three types, each triggered by different light wavelengths- and each waking second of light these cones fire off messages to the brain, which combines incoming signals and produce the visual sensation we refer to as colour vision.
Though vision as a whole is a complex affair, colou calculation is fairly straightforward, in that each type of cone can distinguish about 100 shades, so in total a million combinations are detectable to the human eye. This makes humans trichromats, unlike jusdt about every other mammal, which can distinguish only 10,000 shades and are therefore dichromats.
Only birds and some insects experience visual stimulation on a par with ours, though some go even further, able to detect the ultraviolet part of the spectrum, which we cannot, though it turns out that there are indeed some exceptional people living among us with not three but four types of cone, tetrachromats able to see a hundred million colours, yet with no way of knowing they see far beyond the perceived limits of human vision, nor the facility to describe what they see
For over 20 years now, a Newcastle University neuroscientific team, led by Gabriele Jordan have been seeking out these super-vision people, finally finding one two years ago, in the form of northern England lady doctor - mysteriously referred to only as cDa29 - the first tetrachromat known to science, but almost surely not the last. It was Dutch scientist HL de Vries, in 1948, who first hinted as=t the existence of tetrachromats.
De Vries ran some tests on colour-blind people, speculating that some might be employing a fourth kind of cone to distinguish more colours, but he never really pursued the idea, which lay dormant until, in the 1980s, John Mollon of Cambridge University was studying primate colour vision, becoming interested in De Vries’s notes. Together with Jordan he realized that since four-coned people must be as common as is colour blindness, but tests on potential candidates proved fruitless, because true tetrachromats would never be able to find a satisfactory clour match, with their ability to sense colour gradations far beyond those available to those running the tests.
The question of course, on the lips of everyone, is what must it be like to see through the eyes of cDa29, but unfortunately, the lady in question cannot describe her colour sense to us any more than we can describe colour to someone who only sees in monochrome. So far, it seems that only women ever have the fourth cone, and many of them never know about it, because it remains inactive.
That could be because the natural world does not have enough colour variation to justify the use of it, so these tetrachromats might never need the ability, forever trapped in a world of creatures with lesser powers in the visual sense, unable to bear witness to that unimaginably vast kaleidoscope of colours that must go so far beyond human imagining as to be utterly breath-taking. For now, all we can do is envy cDa29 her truly unique ability, and wish that we could share it.