Vermillion — the brilliant red-orange that illuminates so many Renaissance paintings — was made from cinnabar, a mercury sulphide mineral. It was the most prized red available to European painters for over 600 years. It was also slowly killing them.

Mercury vapour released during the grinding and mixing of pigments causes tremors, personality changes, memory loss, and eventually madness. Art historians now believe that the erratic behaviour and deteriorating mental states of several prominent Renaissance artists — including symptoms that align with mercury poisoning — may have been caused partly by their constant exposure to vermillion.

The painters knew the pigment was dangerous. They used it anyway, because no red sang so brilliantly on wood or canvas. The colour was worth more to them than their health.

St Clair writes: “Vermillion is the colour of blood, of fire, of danger — and its history proves every one of those associations justified.”

Tyrian purple was extracted from the Murex sea snail — a creature found in the Mediterranean. To produce one gram of dye required approximately 10,000 snails. The process involved crushing the snails, extracting a mucus gland, and leaving the material to ferment in the sun for three days — producing a smell described as unbearable, like rotting seaweed and sulphur.

The resulting dye, however, was extraordinary. Unlike every other purple available, Tyrian purple didn’t fade in sunlight — it intensified. The colour deepened with age and exposure. It was effectively indestructible.

Roman emperors decreed that only the emperor could wear full Tyrian purple — death to anyone else found wearing it. When Julius Caesar entered Rome after his Gallic conquests, he wore a full Tyrian purple toga as a statement of supreme power.

The city of Tyre (modern Lebanon) built its entire economy on purple dye production. When Constantinople fell in 1453, the art of true Tyrian purple production was lost. It was not chemically replicated until the 19th century.

In 1775, Swedish chemist Carl Wilhelm Scheele invented a brilliant new green pigment: copper arsenite. It was the most vivid, stable, affordable green ever made. Victorian England went mad for it. Green wallpaper flooded every fashionable home. Green dresses, green curtains, green hat decorations. The colour was everywhere.

It was also made of arsenic.

In damp conditions, a mould grew on the wallpapered walls that converted the arsenic into trimethylarsine — a toxic gas. Families became mysteriously ill. Children in green-wallpapered nurseries developed symptoms doctors couldn’t explain. Some died.

The most famous victim may have been Napoleon Bonaparte on St Helena — his green-wallpapered damp rooms are now believed by some historians to have contributed to his death. His hair samples contain arsenic levels 40 times higher than normal.

The green was so beautiful, so fashionable, and so profitable that even after the danger was widely known, production continued for decades.

In 1979, researchers Alexander Schauss, Gene Baker, and Ron Miller painted a holding cell at the US Naval Correctional Center in Seattle a specific shade of pink — a colour Schauss had been studying for its apparent muscle-relaxing effects. The shade became known as Baker-Miller Pink or “Drunk Tank Pink.”

The results were striking. Violent and erratic behaviour in the holding cell dropped dramatically in the days and weeks after the paint change. Guards reported that even the most agitated prisoners calmed within 15-20 minutes of entering the pink cell.

Subsequent experiments at other institutions replicated the finding. Weight rooms painted Baker-Miller Pink saw immediate reductions in aggression. Psychiatric units reported calmer patients. Some sports teams began painting their opponents’ locker rooms this shade — trying to sap their physical strength and mental aggression before games.

The effect was temporary — about 30 minutes of significant physiological effect. But those 30 minutes, at the right moment, could be decisive.

Birren was hired by a major American manufacturing company in the 1950s to consult on their factory environment. The factory was grey — grey walls, grey floors, grey machinery, grey everything. Accident rates were high. Worker morale was low. Absenteeism was chronic.

Birren redesigned the colour environment: machinery painted in warm but distinct colours to increase visual clarity. Hazardous areas clearly marked in alarming colours. Rest areas painted in calming greens and blues. Corridors brightened with warm neutrals.

One year after the redesign: accident rates dropped 28%. Absenteeism fell measurably. Workers reported feeling less tired at the end of shifts.

Management attributed the improvements to “improved worker attitude.” Birren pointed out that the only thing that had changed was the colour of the walls.

The ancient Egyptian city of Heliopolis — the City of the Sun — contained healing temples specifically designed to use coloured sunlight as medicine. Gemstone windows — slabs of coloured calcite, alabaster, and semi-precious stones — were used to filter sunlight into specific hues that fell on patients lying on treatment tables.

Different chambers were used for different conditions. Red light chambers for lethargy and cold conditions. Blue light for fever and inflammation. Yellow for digestive problems and mental conditions.

Priests trained in chromotherapy maintained detailed records of treatments and outcomes across centuries. When Alexander the Great’s physicians conquered Egypt, they absorbed this knowledge into Greek medicine — which is why Hippocrates describes colour treatments in his writings.

Walker’s research shows that the Egyptian colour prescriptions — arrived at entirely through observation over centuries — align surprisingly well with modern understanding of the biological effects of different light wavelengths.

In 2005, British researchers published a study in the journal Nature analysing the 2004 Athens Olympics results in boxing, taekwondo, Greco-Roman wrestling, and freestyle wrestling — combat sports where athletes were randomly assigned either a red or blue uniform.

Finding: athletes wearing red won significantly more often than athletes wearing blue — across all four sports, across all weight categories, controlling for prior skill level.

The effect was most pronounced in evenly matched contests. Subsequent research found the mechanism operates on both sides: red increases the wearer’s testosterone and dominance behaviour while simultaneously increasing the opponent’s anxiety levels. Red doesn’t just make you feel more powerful — it makes your opponent feel less powerful.

Alter notes a disturbing implication: if uniform colours are randomly assigned at elite competitions, some athletes are being systematically disadvantaged by nothing other than the colour of their shirt.

Teachers have used red pens to mark student work for generations. Alter reports research examining whether this convention has unintended psychological consequences.

In multiple studies, students who received feedback written in red ink rated themselves as having performed worse than students who received identical feedback in other ink colours. Their emotional response to red feedback was measurably more negative — more shame, more anxiety, more likelihood of giving up on the task.

More disturbing: teachers using red pens to grade gave more negative feedback — marking more errors, writing more critical comments — than teachers using other colours on identical papers. The red pen itself appeared to prime a more critical mindset in the grader.

Some schools have since moved to purple and green feedback pens. The quality of teaching hasn’t changed. But the emotional environment of learning has.

In February 2015, a photograph of a dress went viral in a way no image had before. The question was simple: what colour is this dress? Some people saw white and gold. Others saw black and blue. Families sat together staring at the same screen and genuinely could not agree on what they were seeing.

The explanation: the human brain constantly tries to figure out what colour something “really” is by estimating the light source illuminating it. Different brains made different assumptions about the lighting — and those different assumptions led to completely different colour perceptions from the same image.

Badani uses this story to illustrate her central point: colour perception is not objective. It is a construction of the brain, based on context, experience, and assumption. Two people looking at the same object can perceive genuinely different colours — and both be correct according to their own visual systems.

The dress was actually black and blue. But the people who saw white and gold weren’t wrong — they were accurately perceiving what their visual systems constructed from the available information.

A large multinational corporation in the 1960s used the Lüscher test as part of executive assessment. A senior executive being considered for promotion was tested. He was outwardly confident, articulate, and high-performing by every conventional metric.

He placed black first in his colour sequence — the position Lüscher associated with renunciation and deep internal rebellion against constraints. He placed grey second — non-involvement and desire to escape responsibility.

The Lüscher assessment flagged severe compensatory behaviour — projecting an image of control while internally in profound distress and desiring to abandon current responsibilities.

Three months later, the executive abruptly resigned, left his marriage, and moved to another country — a complete life restructuring that those closest to him described as entirely unpredictable.

Lüscher later used this case as an example of the test identifying deep psychological states that conventional assessment tools entirely missed.

For 6,000 years, virtually the entire world’s supply of true ultramarine blue — the most prized blue in art history — came from a single mountain in northeastern Afghanistan: the Sar-e-Sang mines in Badakhshan province. These mines were producing lapis lazuli before the Egyptian pyramids were built.

Finlay travels to Afghanistan — in the early 2000s, with considerable danger — to visit these mines. She climbs to 12,000 feet in the Hindu Kush to reach them. The miners work with hand tools in conditions unchanged for millennia — blasting rock with fire and cold water, then hand-sorting brilliant blue stone from grey matrix.

A single ounce of ultramarine extracted from this stone cost more than gold. When Michelangelo was commissioned to paint the Sistine Chapel, the ultramarine for the ceiling’s blue sections was budgeted separately — a dedicated line item because of its extraordinary price.

Finlay sits in the mine tunnel and processes the fact that every scrap of blue in European medieval religious art — the Virgin Mary’s cloak in thousands of paintings, the sky in countless altarpieces — came through this specific hole in this specific mountain in a country most Europeans couldn’t locate on a map.

When Spanish conquistadors arrived in Mexico in the 16th century, they found Aztec merchants selling small dried seed-like objects — objects that turned out to be the most valuable commodity in the new world after silver and gold: cochineal insects.

Cochineal — tiny scale insects that live on prickly pear cactus — produce carminic acid, the most brilliant, stable red dye ever discovered. It was so superior to any red available in Europe that the Spanish established a monopoly, keeping the source secret for over a century.

When the secret finally leaked in the 18th century, European naturalists were astonished — the most prized red in their world was made from crushed bugs. It took 70,000 insects to produce one pound of dye.

Finlay visits modern cochineal farms in Oaxaca, Mexico, where production continues essentially unchanged. She rubs a handful of dried cochineal between her fingers. Her skin turns brilliant, deep red — carmine — the same red in Renaissance masterpieces, British redcoat uniforms, Stradivarius varnish, and today, still, in lipstick and food colouring worldwide.

Albers walked into his first colour theory class at Yale with a bag of colour samples — pieces of coloured paper. He placed an orange square on a grey rectangle. Then he placed an identical orange square on a bright red rectangle beside it.

“Tell me what colour this square is,” he said, pointing to the first orange on grey.

“Orange,” the students said.

“And this one?” pointing to the orange on red.

Several students hesitated. The orange on red looked yellowish. Almost yellow. The same physical colour now appeared to be a different colour entirely because of what surrounded it.

Albers smiled. “Your eye is lying to you. It always lies.” He placed them side by side without the backgrounds. Identical.

“Everything you think you know about colour is an assumption your visual system is making based on context. Your job as a thinking person is to learn to see what is actually there, not what your brain predicts should be there.”

One former student said: “After Albers, I have never looked at a colour and trusted my first impression again.”

Heller investigates the fascinating evolution of blue’s cultural meaning. In ancient cultures, blue was associated primarily with the sky and water — eternal, distant, and divine. It was the colour of heaven in nearly every religious tradition: Christian heaven, Islamic paradise, Hindu sky god Vishnu’s blue skin, Egyptian lapis lazuli in burial chambers.

In the medieval period, as ultramarine blue became available (from Afghan lapis), it was reserved for the most sacred figures in religious art — primarily the Virgin Mary. Her blue cloak became the single most repeated image in Western art for 400 years. Blue became so saturated with associations of holiness and reliability that these associations transferred to secular life.

Banks and insurance companies began adopting blue in the 20th century specifically because of its deep cultural association with trustworthiness. When Facebook, IBM, Twitter, and LinkedIn all independently chose blue as their primary brand colour — it wasn’t coincidence. It was the accumulated weight of 600 years of blue meaning “sacred, reliable, and trustworthy.”

Heller’s survey found that in every age group, blue was the first colour chosen when respondents were asked to identify “the colour of trustworthiness” — the association is that deep.

Kobayashi’s research revealed fascinating differences between Japanese and Western colour psychology that reflect fundamentally different cultural relationships with colour.

Japanese traditional colour culture contains over 240 named shades of a single colour — green. The relationship between the Japanese language, nature observation, and seasonal colour is so deeply developed that Japanese colour vocabulary for subtle distinctions in natural hues is dramatically richer than any European language.

The Japanese concept of ma — the meaningful empty space between things — applies to colour as well. In Western design, white space is absence. In Japanese design, white space is presence.

When Japanese tech companies like Sony and Honda entered global markets in the 1970s-80s, their product colour choices — clean, restrained, primarily black, grey, and white — were initially considered boring by Western marketing experts. They proved to communicate exactly the values — precision, reliability, sophisticated restraint — that made these brands dominant.