Was the sky blue in ancient Greece? That question is more complicated than it sounds.

A lot of what we think we know about color seems, well, black and white. But it has a surprising history that can challenge our assumptions.

An exhibition at the Lyman Allyn Art Museum explores humanity’s relationship with color from the time of cave dwellers to the present. “Chromatopia: Stories of Color in Art” examines how we perceive the world. Sometimes we can’t see what’s right in front of us.

If you traveled back to ancient Greece and looked up on a clear day, you’d say to yourself, “blue.” But the Greeks thought of color differently. They saw it on a spectrum of light to dark, and blue just wasn’t a concept.

Ancient Egypt was a different story. There, blue was not only recognized, it was practically venerated. The Egyptians produced a blue pigment with which they glazed ceramics, painted on papyrus and decorated walls. The Romans called the shade “Egyptian blue.”

Pigments and dyes, both manufactured substances, drive the use of color in human society. Pigments are ground colored materials, like stone, that don’t dissolve in water, while dyes are soluble.

Both enliven our surroundings, but human perception of color starts with the science of absorbed and reflected light. Biology is also a factor. People with certain defects in their retinas are colorblind, a common disorder. Visitors can test themselves with a chart showing circles of small dots that form numbers. If you’re red-green colorblind, the numbers are invisible.

Thus, our brains are the ultimate deciders of what color something is, using both biological and cultural cues. The brains of the Greeks didn’t deem anything blue even though the color of sky and sea was all around them. In Homer’s famous phrase, the sea was “wine-dark.”

The show’s main idea is printed on a panel that’s the first thing visitors see: “Every color has a story.” Surrounding that thought are squares in different shades that can be lifted to reveal intriguing nuggets about each color.

Scheele’s Green, for example, was a popular choice for decorating early 19th century homes. But the pigment was arsenic-based and sometimes killed people. Indian Yellow was thought to originate in a village where it was made from dried urine of cows fed only mango leaves.

Tyrian Purple, a royal color, was Cleopatra’s costly favorite: Making an ounce of its dye took 250,000 sea snails. Verdigris is the greenish patina that forms on copper exposed to air and water. The Statue of Liberty made it famous.

One of the exhibition’s three galleries goes deeper into stories behind certain colors and the role they’ve played in art.

Vermilion and minium, shades of red, were used in illuminated manuscripts in the Middle Ages, like a French one from c. 1400 that’s on view. Certain letters were highlighted in the colors, carrying on a Roman tradition in which holy days were marked in minium on calendars. That gave rise to the expression “red letter day.”

Lead white was long the best white pigment available. Its smooth, warm tone is seen in the luminous full moon in a 17th century painting called “Moonlit Landscape.” But the problem with the pigment can be guessed from its name: It had toxic ingredients and poisoned workers who made it and women who used it as a cosmetic.

Prussian blue, the first modern synthetic pigment, has a less lethal legacy. In 1842 an English astronomer discovered he could turn parts of chemically treated paper blue while the rest stayed white. Architects, who needed multiple copies of drawings, adapted the phenomenon into the blueprint.

In Japan, the pigment revived the dying tradition of woodblock prints after it was introduced in 1820. Until then, printmakers had used indigo, which faded quickly, but Prussian blue lasted, as seen in a print from the 1850s.

The list of colors and stories goes on. There’s celadon, the bluish-greenish-grayish hue on centuries of Korean pottery; qing, a Chinese color that’s like aqua but with different cultural associations; and orange, a color named for a fruit, or was it the other way around?

The Rolls Royce of pigments was a deep shade of blue from a mountain range in Afghanistan, where lapis lazuli, a blue metamorphic rock, was mined. To European artists who prized the color, Afghanistan was “beyond the sea,” and the Latin for this gave the pigment its name: ultramarine.

Problems creating and shipping ultramarine made it the priciest substance of its kind, and artists reserved it for their most sacred subjects. In particular, the Virgin Mary’s cloak was often rendered in the dazzling color, as seen in a 1495 painting called “Madonna and Child.”

This practice echoes in a surprise about color from much later: the convention of “pink for girls, blue for boys.” That’s an American idea but an unexpectedly recent one. Consider this quote from a 1918 trade publication for children’s clothing:

“The generally accepted rule is pink for the boy and blue for the girl. The reason is that pink, being a more decided and strong color, is more suitable for the boy, while blue, which is more delicate and dainty, is prettier for the girl.”

The exhibition notes than pink, a shade of red, once evoked blood and battle and symbolized Christ’s self-sacrifice in medieval paintings. And the notion of blue as feminine can be traced back to those ultramarine cloaks.

Blue is what sparked the idea for “Chromatopia,” said Jane LeGrow, the Lyman Allyn’s registrar and director of exhibitions, who curated the show. Twenty years ago she attended a Smithsonian lecture on the color’s history, and it lit her imagination.

Creating an exhibition that’s a popular history of color allowed her to use items in the museum’s collection, like celadon pottery, that aren’t often seen. And it offered wide appeal.

“Everybody has a feeling about color,” she said.

One of the surprises she encountered was how much of the story was tied to industrial practices that had nothing to do with art. For example, she said, a German chemist’s unsuccessful attempt to develop a bright yellow dye was later revisited and led to military use of the substance, known as TNT, as a weapon.

If vivid pigments transformed art in earlier times, by the 20th century art itself was changing. With the emergence of abstract painting, sometimes color became the subject.

The exhibition’s final section includes some imponderable examples of this, like a 1997 painting by Richard Tuttle called “Colors,” which consists of a black rectangle inside a yellow rectangle. Or “Two Yellows,” a 1959 work by Gene Davis that shows alternating stripes of what, despite the title, look like orange and green.

More interesting are recent attempts by a few artists to essentially own a particular color. In 2016, sculptor Anish Kapoor bought exclusive rights to Vantablack, the darkest manmade substance. This raised the hackles of other artists, who questioned the ethics of color exclusivity.

Earlier, French artist Yves Klein trademarked a hue he called International Klein Blue, or IKB.

Despite such cases, vivid colors are more accessible today than in former times, when they were the exclusive province of the wealthy, LeGrow said.

“We look around today, and we can have literally any color we want,” she said.

j.ruddy@theday.com

IF YOU GO

What: “Chromatopia: Stories of Color in Art”

Where: Lyman Allyn Art Museum, 625 Williams St., New London

When: Through March 5

Hours: 10 a.m.-5 p.m. Tuesday-Saturday, 1-5 p.m. Sunday

Admission: Adults $12, seniors $9, students $5, children under 12 free.

Information: lymanallyn.org