The color blue is in the middle of a mystery that links biology, psychology, art, and linguistics. Many believe that the way we see blue – that is, as a distinct color – is actually a modern development. For those in the past, the concept of the color blue might not have existed at all. Even some cultures today don't see blue in the same way as people in the West.

This fact may seem impossible but it's true. You may argue that the sky is blue and so is the sea, but it's possible your experience is putting a label on it. You might say that blue is real but to misquote Morpheus in The Matrix, “'real' is simply electrical signals interpreted by your brain.” As humans, we have many examples that reveal to us that our brains are not perfect boxes of logic, but instead full of biases and easily tricked. One of the best recent examples of this is the infamous dress photo: Is it white and gold or black and blue?

Discussions on the color blue often start with the observations by William Gladstone, who served as British Prime Minister more than a century ago. In the third volume of “Studies on Homer and the Homeric Age”, Gladstone discusses the use of color in the Greek poet's work, specifically the lack of variety. For example, there is no mention of blue at all. To get to the bottom of this, Gladstone used examples of things we know to be blue to work out the Greek term for the color.

This is the section that launched a thousand research papers. Gladstone reported that Homer used the word “iron” and the word “copper” to describe the sky. The adjective employed in the Iliad to describe the sea is even more puzzling – "oínopa pónton", literally "wine-face sea". Gladstone interpreted this as “wine-dark” in color. Others have since seen it as “wine-like”, suggesting that it might have to do with the sloshing of wine similar to the rough sea, rather than the color.

While the true meaning of the description remains uncertain, it makes sense that descriptions in the ancient world were limited when it came to color. In the animal and plant kingdoms, blue is rare. Even blue pigments and blue gems and rocks were rare in antiquity. People back then didn’t need as many adjectives for color as modern times because there was nothing in their life in a hue beyond what they used. Blue didn’t appear in Chinese stories, the Icelandic Sagas, or ancient Hebrew versions of the Bible. The Ancient Egyptians, however, did have a word for blue. They were also the only ancient culture to develop a blue dye and commonly use blue in jewelry and ornaments.

Linguistically, the color blue appeared late in Western languages. In several languages, including Japanese, Thai, Korean, and Lakota Sioux, the word for blue is used to describe color shades that include green. In Welsh, the word for blue came from the word for green, so that the literal translation of grass (glasswelt) is blue straw.

Several hunter-gatherer cultures living today similarly have a single word to describe shades of green and blue. A particularly interesting example is the Himba people, an indigenous population in Northern Namibia. They don’t have a separate word to distinguish blue from green, so when tested on distinguishing two colors that are obviously different to Western eyes, they were not very successful.

For the Himba, shades that we would describe as green have different names, and researchers have found that some hues that are indistinguishable to most Westerners are dramatically different to the Himba (see the video below from BBC's Horizons). Perception, not just beauty, seems to be in the eye of the beholder.

The connection of blue to other colors is not exclusive to green. In Indo-European languages, blue has its roots in a word that describes colors such as brown, gray, and yellow. This connection is particularly clear in Slavic languages, where the word for blue (plavi, polovyi, plowi, etc.) can also be used to describe blond hair.

The entire field of color perception in different languages is full of examples of words that correspond to specific shades that have no equivalent in English. But as languages evolve to incorporate more colors, these shades become distinct. Blue is a broad church, from cyan and ultramarine to azure and navy.

While we use language to describe what we see in the world, it appears that language also shapes our perception of reality. Perhaps until we learn or invent new words, we can’t easily describe or even distinguish between certain hues. So don't be too disheartened if you're told a sweater is not blue, turquoise, or lapis, but actually cerulean.