"Human vision is trichromatic," says professor Andrew Stockman, a UCL colleague of Lotto's. "Like a colour television." We have three different colour receptors, cones, in our eyes, each designed to pick up different wavelengths of light. These are red, green and blue. Most mammals, apart from a few of our fellow apes, have two, and so do most colour-blind people, meaning they can only detect green and blue wavelengths. If we had only one receptor, we'd see the world in something like black and white.
This is the product of billions of years of evolution. Long before our ancestors had anything you'd call an eye, back when they were single-celled organisms, they had some basic light sensitivity, and would have been able - to some degree - to detect differences between long-wavelength and short-wavelength light. This would have allowed them to tell when it was daylight (blue light) and sunset (red light). Later, as lifeforms grew more complex, we developed more sophisticated techniques for more sophisticated purposes.
"The whole point of colour vision is not to inspire poets, but to allow contrast detection," says Russell Foster, professor of circadian neuroscience at the University of Oxford. "You've got a much better chance of detecting an object against a background if you have colour vision." Birds are the masters at this, he says - they are tetrachromatic, having four colour detectors, and would see things that we see as a single red as an infinite, glorious wash of colours. (Mantis shrimp, a kind of predatory marine crustacean, have 12 detectors, but for some reason do not seem to be better at distinguishing colours than we lowly humans.) Unlike birds, though, mammals are descended from small, timid creatures who scurried around avoiding dinosaurs - and, crucially, were nocturnal. Our ancestors had far less use for colour detection, which is much harder at night. It was only after the death of the dinosaurs 65 million years ago that our forebears ventured out into the daylight, and it is only 30 or 40 million years or so since a mutant ape developed a third colour receptor.
Nonetheless, the wavelength of the light around us has affected us since the dawn of life, and it still does. Foster, who researches the effect of light on sleep, tells me that our circadian rhythms - our "biological clock" - are profoundly affected by not just the brightness of the light we're exposed to, but the colour of it. He was behind the discovery of a previously unknown cell in the optic nerve which acts as a sort of photon-counter, keeping track of how much light has hit it in the last few minutes. It is especially sensitive to blue light - specifically, the blue of a blue sky. If you're exposed to light of this colour, it will make you more alert. "Blue light keeps us awake far more effectively than red light," he says; "there are apps, now, that change your lighting before you go to bed, to get you ready for sleep."
But earlier, we saw that red made us perkier, and blue calmed us down. This is because, as Lotto says, context is everything; red can be friendly when it's associated with a ketchup bottle and baleful when associated with blood.
Lotto spends much of his time creating optical illusions to demonstrate how humans see and perceive colour, and the impact of context upon it. "I can take a grey patch, and cause you to see any colour in it," he says. "I can make you see blue or yellow, depending on what surrounds it. When I change your perception of it, what I'm changing is the meaning of the information, I'm not changing the physics of the information itself.
"If I make a patch appear as if it's under shadow, you'll see it as being lighter than if I make the same patch appear as if it's on a dark background. That's basically what your brain is constantly doing." The illusions are remarkable to look at: two patches of identical colour, brightness and shape will appear as utterly different colours to our eyes, because of simple tricks of perspective and shade which make one look as though it's under red light, or another under shadow. These illusions are unsettling to see, at least for me: they undermine my sense of being grounded in reality.
But we're not uniformly sensitive to these illusions; again, context matters. "How powerful people feel alters their perception of colour," says Lotto. "If I make you feel a bit more powerful, a little more in control, the strength of the illusions that I make decreases. If I put you in a state of powerlessness, the strength of illusions increases." It's because we're more sensitive to context when we feel out of control; we become less comfortable with uncertainty.
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Similarly, he says, these illusions are more effective on people from eastern cultures, where social context is all-important. "The people around you are far more important in the east, whereas in the west we're far more individualistic."
It gets more complex: "context" can mean things as apparently unrelated as whether you're feeling morally compromised. A 2011 study published in the journal of the Association for Psychological Sciences found that people who had been asked to recall something unethical they'd done tended to judge the room they were in as darker than those who'd been asked to remember something ethical.
There's even some indication that the words we use to describe colour affect our ability to see it. Benjamin Whorf, a linguistic theorist, claimed that our language limits our perception: if our language lacks a word for something, we find it harder to think about that thing.
The Whorfian hypothesis has been largely discredited - after all, if we really couldn't think about things we didn't have a word for, we wouldn't need to come up with new words; English didn't have a word for "schadenfreude" until quite recently, but we understood the concept well enough. Neverthless, experiments have shown that societies such as the Tarahumara tribe in Northern Mexico, which lack different words for "blue" and "green", find it harder to find the odd one out in a group of greenish-blue squares. Meanwhile, the fact that we distinguish indigo and violet as separate colours is largely down to Newton, who named and split up the colours of the rainbow completely arbitrarily.
The cultural contexts and meaning of colours has been picked up, of course, by marketers, as suggested by the title of a paper in the Journal of the Academy of Marketing Science, "Exciting red and competent blue: the importance of colour in marketing". White is "purity, cleanness, simplicity, hygiene, clarity and peace"; black is "sophistication, glamour, status, elegance, richness and dignity". Purple is status, pink is femininity, and, of course, blue suggests competence while red is exciting. Using these colours in your brand or logo, apparently, will subtly instil those messages in potential customers' minds.
A lot of these highly specific claims are probably hogwash, as another paper, in the journal Color Research & Application, made clear in its own title: "Colour psychology and colour therapy: Caveat emptor". The evidence-based hypotheses are often hard to tease out from the mystical or made-up nonsense, writes its author, Zena O'Connor: "The information available is often presented in an authoritative manner exhorting the reader to believe a range of claims such as red is physically stimulating and arousing and blue is calming and healing. However, evidence is rarely cited and, when it is, it's often in reference to findings that are inappropriately generalised or out-of-date." But even after the dubious claims have been weeded out, colour clearly still has a profound impact on our mental life.
An obvious question is how much of this impact is innate, and how much is culturally learnt. For instance, the study into the psychological effects of pink, mentioned above, was carried out by Alexander Schauss in the 70s. It showed that of 153 male prisoners put in cells painted pink, 98.7 per cent were weaker after being in the pink cells for only 15 minutes - presumably because of associations between the colour pink and femininity. But the pink has only been associated with girls for 70 years or so; would the same result have been found in Victorian times? Probably not. But the red light/blue light distinction that Foster refers to must be written deep in our genes.
The allure of red certainly crosses cultural boundaries. A 2012 study conducted in Burkina Faso, in West Africa, where red has explicitly negative associations, still revealed it to be a sexual trigger. Some scientists believe that we and other primates such as chimps and gorillas developed the ability to detect the colour red because of a common characteristic: bare-skinned faces. Suddenly, we could "read" the all-important expressions of anger, dominance, confidence and sexual readiness on the faces of those around us.
Since we know that "colour" is a product of how our eyes interpret electromagnetic radiation, we know that it's not an attempt to represent the world as it really is. Natural selection doesn't care whether you have a true representation of the universe. It only cares if you can find food and attract mates and avoid predators. "Your perception of colour either helped you behave usefully towards this thing, or it didn't," Lotto says; either it helped you decide whether to eat something, to mate with it, or to run away from it, or it didn't.
All our perceptions, then, are grounded in our evolutionary history, which provides us with some of our underlying assumptions, and our personal, culture-infused life history, which provides us the rest. Colour is simply a useful way that our brains have come up with for representing the world - and what we learn from colour vision applies to the rest of the brain's interaction with the world.
"And that, to me, is why colour vision is wonderful," says Lotto. "You begin looking there, and it opens up all these other questions, and reveals what the brain is trying to do."
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