Blue: how did blue, long the rarest color, become the world's favorite?

Short answer

Blue was everywhere, in the sky and the sea, but it couldn't be held in the hand: nature offered very little blue matter that could be easily gathered and turned into a lasting dye. So humanity got its blue from an expensive stone, a labor-intensive plant, or a laboratory. As blue grew cheaper and spread everywhere, it also became everyone's favorite; today, surveys in many countries name blue as the most loved color.

Science — why is blue so rare?

The sky's blue isn't a substance but a process: it arises from molecules in the air scattering short-wavelength light, and that's the subject of KE-02. The sea's blue has a separate and surprising source: water itself is faintly blue. As water molecules vibrate, they absorb a very small share from the red end of the spectrum. In a glass of water this difference is invisible, but once light travels through several meters of water, enough red is lost that blue remains. Both are blues you can't touch or put in a container: you can't fill a jar with the sky's blue, and the sea's blue disappears in a handful of water.

This difficulty shows up clearly in the living world. Most blue bird feathers and blue butterfly wings contain no blue pigment at all; the blue arises from light interfering within extremely fine structures. The physics of this structural color is covered separately in MA-08. In plants, blue is most often a special arrangement of anthocyanins, the same molecules that otherwise produce red and purple tones.

In the human body, too, blue is an illusion. The veins beneath the skin look bluish, but the blood inside them is dark red: red light sinks deeper into the tissue and gets absorbed there, while blue light bounces back from closer to the surface. This effect is more visible in light skin; in dark skin it's weaker, because melanin absorbs the light before it has a chance to do this.

In short, blue was the color the eye saw every day but the hand found hardest to hold. This scarcity set blue's history apart from every other color's: every way of obtaining it required its own invention.

History — how was blue obtained?

It's no surprise that the earliest known human-made pigment turns out to be blue: what nature didn't offer ready-made, people made in a kiln. TK-02 follows the recipe for this material, known as Egyptian blue, and its later disappearance. For centuries after that, Europe's most prized blue was ultramarine, ground from lapis lazuli brought down from the mountains of Afghanistan; its journey and its place in art are the subject of TK-04.

Cloth, though, needed a different blue. Indigo, extracted from the indigo plant, was the foundation of dyeing in many traditions from India to West Africa, and it eventually became the color of blue jeans. The story of this dye — from a green leaf, to a yellowish bath, to blue once it meets the air — is told in TK-06.

The real breakthrough came by accident, in Berlin at the start of the 18th century. A dye maker trying to produce a red pigment ended up with a dark blue instead, because the material he was using had been contaminated with an animal substance. This pigment, named Prussian blue, is considered the first synthetic pigment of the modern era, and it was far cheaper than ultramarine.

When Prussian blue reached Japan a century later, woodblock print masters embraced it, because it resisted fading better than the traditional plant-based blues. With the development of synthetic ultramarine and then synthetic indigo in the 19th century, blue stopped being an expensive privilege.

Blue's laboratory story continues today. In 2009, a team at Oregon State University working on electronic materials pulled an unexpectedly bright blue compound out of a kiln. Made of yttrium, indium, and manganese, this pigment was named YInMn blue after the elements' symbols, and it was introduced as a new blue discovered two centuries later. Why it takes years for a pigment to go from the lab to the market is the question MA-07 asks.

Culture — what did blue mean?

In Europe, blue's standing changed over time. According to historian Michel Pastoureau, blue was considered an unimportant, even somewhat foreign color in ancient Rome. In the Middle Ages, the Virgin Mary's cloak being painted blue, and blue's use in royal coats of arms from the 12th century on, moved it into the colors of the church and the court. Pastoureau's account is a historian's interpretation and focuses specifically on Europe; in the same period, blue's story in other cultures is different.

Turkish has its own blue story, too. In Old Turkish, the sky's color was called gök, the word for the sky itself; the word Turkish uses today, mavi, was taken from an Arabic word meaning "of water, water-colored." The same color's name comes from the sky in one language and from water in the other. Blue's widespread use in tilework in Anatolia forms a separate tradition of its own. The early period of the İznik tile workshops is known for a palette that worked in cobalt blue on a white ground; how turquoise, green, and a raised red were added to this palette is told in TK-10. Blue's standing was thus built not only in the courts of Europe, but through separate paths in the workshops of other regions, too.

Today — where is blue found today, and at what cost?

Today blue is cheap and everywhere: in blue jeans, corporate logos, interfaces, work uniforms. A color once bought in quantities barely enough for Mary's cloak is now one of the colors banks and technology companies choose most often. Common claims that a color "gives" trust, order, or calm, though, usually rest on weak evidence; how to test this is the subject of PS-01.

Blue is also a color tied to rules today. In international safety signage, a blue circle means something must be done: wear a helmet, put on gloves. In a system where red prohibits and yellow warns, blue is the color of obligation; this visual language is covered in detail in EN-07. Blue being considered the color for boy babies, on the other hand, is a fairly recent coding; how this pairing took hold, and how reliable the often-quoted old magazine passages about it really are, is discussed in TK-18. In short, blue's meaning today isn't a single thing but a bundle that shifts with context.

Blue's most striking feature today is how much it's loved. In surveys across different continents, the answer to the favorite-color question keeps coming up blue.

Why blue is loved this much is still an open question. One theory proposes that people love colors they associate with good experiences, like clean water and a clear sky; the strength and limits of this approach are discussed in PS-03. For anyone who knows the history, the irony is plain: the hardest color to obtain became the easiest color to love.

Common misconception

Summary

1. Blue is everywhere in nature, in the sky and the sea, but lasting blue pigment is rare; blue in living things is most often structural, or a complex molecular assembly.
2. Humanity obtained blue from a kiln (Egyptian blue), a stone (ultramarine), a plant (indigo), and a laboratory (Prussian blue); synthetic blues made the color cheap.
3. Blue's standing rose in Europe in the Middle Ages; today it's the most loved color in many countries, but why it's loved this much is still debated.

Test yourself

1. (Easy) Which blue is considered the first synthetic pigment of the modern era?
2. (Easy) What does the Turkish word mavi come from?
3. (Medium) Where will you first notice this color around you today, and what will you now see differently?
4. (Medium) Why can't the cornflower's blue be explained by a single pigment?
5. (Hard) What connection can be drawn between blue being one of the hardest colors to obtain and its being the most loved color today?
6. (Hard) What limit should you keep in mind when reading Pastoureau's history of blue?

Answers

1. Prussian blue; it was discovered by accident around 1706 in Berlin ("History").
2. From an Arabic word meaning "of water, water-colored"; in Old Turkish, the same color was called gök ("Culture").
3. There's no single correct answer: it could be a pair of jeans, a logo, a tile, or the sky. A strong answer identifies where the blue in front of you comes from (pigment, dye, screen light, or scattering) and says which side of it you're noticing for the first time after this lesson ("Today").
4. The blue arises from a complex formed by six anthocyanin and six flavone molecules with iron, magnesium, and calcium ions; on their own, these anthocyanins don't produce blue ("Science").
5. Because blue was scarce and expensive for so long, it gained a valuable meaning; once synthetic pigments made it cheap and spread it everywhere, these positive associations and its availability may together have made it a favorite. The exact reason for this love, though, is still an open question ("Today").
6. His account is a historian's interpretation and focuses specifically on Europe; blue's story in other cultures is different ("Culture").

Sources

• Shiono, M., Matsugaki, N., and Takeda, K., "Structure of the blue cornflower pigment," Nature 436: 791, 2005.
• Cultural Heritage Science Open Source, "Prussian Blue: The First Synthetic Pigment."
• Pastoureau, M., Blue: The History of a Color, Princeton University Press, 2001.
• YouGov, "Why is blue the world's favorite color?", May 2015.
• Braun, C. L., and Smirnov, S. N., "Why is water blue?", Journal of Chemical Education 70(8), 1993.
• Nişanyan Sözlük, entry for mavi.

Next step

TK-04 opens up blue's most expensive form: it covers the stone's journey from mountain quarries to European workshops, this blue reserved for sacred figures, the synthetic ultramarine that eventually made it cheap, and why painters reserved this blue only for their most important figures. PS-03, meanwhile, takes up today's question: why blue is such a widespread favorite, discussing it alongside ecological valence theory, object associations, and the effects of age and culture.