## Blue: Ten Surprising Facts about the Color Blue

We all know the sky is blue, the ocean is blue, and the flag is (red, white, and) blue. Some of us have blue eyes, or blue blood, or are in a blue mood. And chances are you’re wearing something blue today. But how much do you know about the history of the color blue?

In Blue: The History of a Color, historian and symbologist Michel Pastoureau takes readers through the different meanings and uses of blue throughout Western history. Pastoureau’s fascinating anecdotes and lavish illustrations remind us that “color is first and foremost a social phenomenon.”

Originally published in 2000 as the first title in Pastoureau’s acclaimed series on the histories of colors, Blue is now back in print.

Here are ten surprising facts about blue:

1. In ancient Rome, blue was associated with barbarians. Wearing blue was looked down on as a sign of eccentricity or mourning, and blue eyes were considered a sign of bad character or a physical deformity.

2. The uses and meanings of blue in Europe shifted sharply when it became the color of Mary’s cloak during the development of the cult of the Virgin in the twelfth century. From depictions of Mary, blue spread to other religious imagery.

3. Because of the low usage of blue in ancient Greek and Rome, researchers in the 1800s wondered if the ancient Greeks and Romans could even see the color blue. (They could.)

4. In the twelfth and thirteenth centuries, merchants of woad (a blue plant-based dye) and madder (a red plant-based dye) competed fiercely and even violently to discredit each other’s colors.

5. During the Reformation, blue was classed with white, black, gray and brown as an “honest” color.

6. Blue was the symbolic color of the French Revolution, but France had trouble maintaining a large enough supply of indigo dye to keep its military dressed in blue. In 1829, infantrymen were ordered to wear red pants instead. They switched back to blue, however, in 1915, after the visibility of their bright red pants led to mass casualties in the first year of the Great War.

7. Goethe’s 1774 novel The Sorrows of Young Werther popularized blue coats for young men. The character Werther wears a “simple blue dress coat” with a yellow vest and trousers. Goethe saw blue and yellow as symbolic opposites, with blue being positive (active, warm, and bright) color and yellow being negative (passive, weak, and cold).

8. Between 1910 and 1950, black uniforms and clothing gave way to navy blue in one of the most important fashion events of the century.

9. Levi Strauss denim jeans were the first garments to have the brand name displayed on the outside. This was done to distinguish them from competing blue jeans brands Lee and Blue Bell (now Wrangler).

10. More than half of American adults today say blue is their favorite color. Pastoreau suggests that this statistic be taken with a grain of salt, even as he cites it as evidence of just how far blue has come since antiquity.

## 12 Facts from Red: The History of a Color

Over the years, the color red has represented many things, from the life force and the divine to love, lust, and anger. Throughout the Middle Ages, this vibrant color held a place of privilege in the Western world. For many cultures, red was not just one color, but rather the only color worthy enough to be used for social purposes. In this beautifully illustrated book, Michel Pastoureau, the acclaimed author of Blue, Black, and Green, illuminates red’s evolution through a diverse selection of images that include the cave paintings of Lascaux, Renaissance masters, and the modern paintings and stained glass of Mark Rothko and Josef Albers. How much do you know about the history and symbolism of red?

In many languages, the same word can mean “red,” “beautiful,” and “colorful” all at once. Coloratus in classical Latin and colorado in modern Castilian can both mean “red,” or simply “colored.”

In Russian, the word for “red” shares a common root with the word for “beautiful.” Krasnyy and krasivy respectively.

The image of a white, somber Greece, inherited from historians and theoreticians of neoclassicism, is false. The Greeks made use of vivid, contrasting colors.

Vases with red figures appeared in Athens abut 530-520 BCE, presenting a background painted uniformly black with figures worked in relief that took the red color of the clay upon firing. The drawings were more precise than what had come before, the realism greater, and the subjects more varied.

In ancient Rome, cinnabar was a popular medium for making red despite its high price and dangerous nature—it is a powerful poison. For example, it was present throughout Pompeii in wall painting.

Dyeing, like painting, was first achieved in ranges of red.

Henna is a bush that grows in warm regions whose leaves when dried and reduced to a powder provide a colorant for dyeing in red or in reddish brown.

Throughout their history, Roman dyers seem to have been most skilled in the range of reds, purples, oranges, and yellows. Celtic and German dyers were most successful with greens and blues.

The flag of the Crusades was white with a red cross, symbolically representing the blood of Christ and representing the blood that the soldiers were willing to spill to free the Holy Lands.

In the Middle Ages, judges were most often dressed in red, the color of their delegated power and their function: to state the law and render judgments in the place king, prince, city or state. The angel who expelled Adam and Even from Paradise was depicted in red clothing: an angelic dispenser of justice.

In the medieval period, red was both feminine and masculine—virile and full of grace. On the feminine side, it represented love, radiance, and beauty. For men, it was the color of courage and power.

**

For more on the history and symbolism of this vibrant color, read Red: The History of a Color. You can also enter our giveaway for a chance to win a copy, and be sure to share your red photos with us on Twitter and Instagram using the hashtag #PUPRed.

Michel Pastoureau is a historian and director of studies at the École Pratique des Hautes Études de la Sorbonne in Paris. A specialist in the history of colors, symbols, and heraldry, he is the author of many books, including Red: The History of a Color.

## Happy Valentine’s Day from PUP

Valentine’s Day is the day we all show the people we care about how special they are to us. This year, we’re celebrating with the publication of Michel Pastoureau’s Red: The History of a Color, because red is the color of love! Enter for a chance to win a copy of your own on Goodreads or by submitting your own red pictures using the hashtag #PUPRed on Twitter and Instagram.

## Red: The History of a Color Valentine’s Giveaways

### Got red? We’re excited to announce two new giveaways!

Throughout the centuries, the color red has symbolized many different things, from masculine power, strength, and courage to the immorality of the Catholic Church. On Valentine’s Day, red is a universal symbol of romantic love. During the month of February we’re hosting a Goodreads giveaway of Red: The History of a Color, Michel Pastoureau’s beautifully illustrated tour of centuries of red symbolism. Enter for a chance to win yours on Goodreads. We’ll select three random winners on March 1.

And for another chance to win, show us your red! Just share your red photos with us on Twitter and Instagram using the hashtag #PUPRed, and we’ll be randomly selecting a winner among those participants on Valentine’s Day.

## Announcing Red: The History of a Color

In Red: The History of a Color, Michel Pastoureau writes that to speak of the “color red” is almost a redundancy. The “archetypal color”—and the first that humans mastered and reproduced for painting and dyeing—red has conjured courtly love, danger, beauty, power, politics, and hell. From the paleolithic age through Greco-Roman antiquity to the present, red has represented many things, so many, in fact, that in several languages, the word means “beautiful” and “colorful” at once.

In this gorgeously illustrated book, Pastoureau, the acclaimed author of Blue, Black, and Green, now masterfully navigates centuries of symbolism and complex meanings to present the fascinating and sometimes controversial history of the color red. Take a tour of Red: The History of a Color, and read on about two upcoming giveaways.

For a chance to win one of three copies up for grabs, enter our Goodreads Valentine’s giveaway, which will be running from February 1 to February 28. And for a second chance to win, share your own creative red photos with us on Twitter and Instagram using the hashtag #PUPRed—we’ll be giving another book away to a random participant on Valentine’s day.

## Nicholas Higham on Mathematics in Color

We are excited to be running a series of posts on applied mathematics by Nicholas Higham over the next few weeks. Higham is editor of The Princeton Companion to Applied Mathematics, which is out this month. A slightly longer version of this post on color in mathematics can be found on Higham’s blog, and it has been cross posted at John Cook’s blog, The Endeavour. —PUP Blog Editor

Color is a fascinating subject. Important early contributions to our understanding of it came from physicists and mathematicians such as Newton, Young, Grassmann, Maxwell, and Helmholtz. Today, the science of color measurement and description is well established and we rely on it in our daily lives, from when we view images on a computer screen to when we order paint, wallpaper, or a car, of a specified color.

For practical purposes color space, as perceived by humans, is three-dimensional, because our retinas have three different types of cones, which have peak sensitivities at wavelengths corresponding roughly to red, green, and blue. It’s therefore possible to use linear algebra in three dimensions to analyze various aspects of color.

## Metamerism

A good example of the use of linear algebra is to understand metamerism, which is the phenomenon whereby two objects can appear to have the same color but are actually giving off light having different spectral decompositions. This is something we are usually unaware of, but it is welcome in that color output systems (such as televisions and computer monitors) rely on it.

Mathematically, the response of the cones on the retina to light can be modeled as a matrix-vector product $Af$, where $A$ is a 3-by-$n$ matrix and $f$ is an $n$-vector that contains samples of the spectral distribution of the light hitting the retina. The parameter $n$ is a discretization parameter that is typically about 80 in practice. Metamerism corresponds to the fact that $Af_1 = Af_2$ is possible for different vectors $f_1$ and $f_2$. This equation is equivalent to saying that $Ag = 0$ for a nonzero vector $g =f_1-f_2$, or, in other words, that a matrix with fewer rows than columns has a nontrivial null space.

Metamerism is not always welcome. If you have ever printed your photographs on an inkjet printer you may have observed that a print that looked fine when viewed indoors under tungsten lighting can have a color cast when viewed in daylight.

## LAB Space: Separating Color from Luminosity

In digital imaging the term channel refers to the grayscale image representing the values of the pixels in one of the coordinates, most often R, G, or B (for red, green, and blue) in an RGB image. It is sometimes said that an image has ten channels. The number ten is arrived at by combining coordinates from the representation of an image in three different color spaces. RGB supplies three channels, a space called LAB (pronounced “ell-A-B”) provides another three channels, and the last four channels are from CMYK (cyan, magenta, yellow, black), the color space in which all printing is done.

LAB is a rather esoteric color space that separates luminosity (or lightness, the L coordinate) from color (the A and B coordinates). In recent years photographers have realized that LAB can be very useful for image manipulations, allowing certain things to be done much more easily than in RGB. This usage is an example of a technique used all the time by mathematicians: if we can’t solve a problem in a given form then we transform it into another representation of the problem that we can solve.

As an example of the power of LAB space, consider this image of aeroplanes at Schiphol airport.

Original image.

Suppose that KLM are considering changing their livery from blue to pink. How can the image be edited to illustrate how the new livery would look? “Painting in” the new color over the old using the brush tool in image editing software would be a painstaking task (note the many windows to paint around and the darker blue in the shadow area under the tail). The next image was produced in
just a few seconds.

Image converted to LAB space and A channel flipped.

How was it done? The image was converted from RGB to LAB space (which is a nonlinear transformation) and then the coordinates of the A channel were replaced by their negatives. Why did this work? The A channel represents color on a green–magenta axis (and the B channel on a blue–yellow axis). Apart from the blue fuselage, most pixels have a small A component, so reversing the sign of this component doesn’t make much difference to them. But for the blue, which has a negative A component, this flipping of the A channel adds just enough magenta to make the planes pink.

You may recall from earlier this year the infamous photo of a dress that generated a huge amount of interest on the web because some viewers perceived the dress as being blue and black while others saw it as white and gold. A recent paper What Can We Learn from a Dress with Ambiguous Colors? analyzes both the photo and the original dress using LAB coordinates. One reason for using LAB in this context is its device independence, which contrasts with RGB, for which the coordinates have no universally agreed meaning.

## The Princeton Companion to Applied Mathematics

Nicholas J. Higham is the Richardson Professor of Applied Mathematics at The University of Manchester, and editor of The Princeton Companion to Applied Mathematics. His article Color Spaces and Digital Imaging in The Princeton Companion to Applied Mathematics gives an introduction to the mathematics of color and the representation and manipulation of digital images. In particular, it emphasizes the role of linear algebra in modeling color and gives more detail on LAB space.