Occasionally I like to think about the fact that no two human beings have exactly the same experience of color when looking at the same object. Same wavelengths, sure, but there’s no way to know what someone else really sees when they look at a bright red barn. Color isn’t totally subjective, but it’s far from objective either.

This is the first of a few posts on color. They’re all more related than I thought they would be when I started doing research for them, which is really exciting and has resulted in me reading long articles about color theory at night long after I should be asleep. (You’re welcome, dear readers. I do it all for you.)

If you’ve read Homer at some point, by choice or under duress, you may have come across some interesting poetic descriptions. One of the most famous is a reference to the “wine-dark sea.” This sounds pretty, but it doesn’t seem to make a lot of sense if you think about it. Whether we’re talking red, white, or rosé, no wine is the color of the sea.

Of course, you can also take it as a metaphor—the sea may be dark, rich, and mysterious, like wine—but this isn’t the only odd color description in the Iliad and the Odyssey. At different points, the sky is described as bronze, sheep as violet, and honey as green. Some of these could just be fantastical touches or poetic license—which is more unbelievable, violet sheep or the cyclops who keeps them? Still, the whole thing adds up to a pretty strange picture of color.

Studying the specific terms used by Homer, scholars see a lot of references to light and dark things, and sporadic uses of red, yellow, and green. However, in both epic poems, there is not one case of a word that they can identify with the color blue.

We can give Homer a pass on this, since legend says he was blind. (Assuming that he was in fact a person, of course, and not a whole school or poets or an even broader catchall name for anonymous poets.) It seems unlikely that wrong descriptions would have been approved and passed on by his sighted listeners, though.

Historians have come up with various theories to explain the color weirdness, including the possibility that the ancient Greeks were all colorblind (those who weren’t completely blind, naturally). However, there’s another explanation, which seems both pretty sensible and totally unfathomable to modern minds. This theory is that the Greeks of Homer’s time, rather than suffering from mass colorblindness, simply didn’t yet have the words to describe blue as a distinct color.

This sounds preposterous to us, because in the languages most of us speak today, we can’t imagine not having a word for what seems like such a basic color. Surprisingly, it starts to sound a lot less crazy when we look beyond Homeric Greek to other ancient languages and cultures. A 1969 study of languages around the world suggested that overall, there’s a certain flow to the development of color terms and distinctions.

At first, the study claimed, most languages only distinguish between light and dark. This is definitely not the same as white and black, since it includes all colors based on their lightness or darkness (or warmness and coldness) instead of dividing them by hue. What happens next generally is that red splits off from the warm colors and gets its own word. After this comes either yellow or green, then the other one. Then, finally, blue makes an appearance, emerging from the general dark/cold color palette. Secondary colors like purple, brown, and orange are specified sometime afterward.

Many scholars agree generally with this scheme of development, though there are some who feel the evidence behind the original theory was unconvincing or unprofessionally analyzed. There have been other studies since the 60s that agree with the broad strokes of the theory, however, including the collection and analysis of the World Color Survey database.

I came across a fun paper from 2012 that attempted to answer some of the questions about trends in color names using computer modeling. Basically, artificial agents or simulated intelligences had to get each other to distinguish between different numbers (representing different colors) by giving them names and coming to a social consensus on those names and their ranges of meaning. By programming the agents to be sensitive in different number ranges similar to human visual limitations, researchers reproduced almost the same order of color terms found in human studies (violet seems to split from red earlier, but otherwise they agree).

Let’s tackle one of the big questions about color hierarchy: why does it happen this way? Biology and history offer a few clues. (Blue’s clues, if you will. …You won’t? Yeah, me neither.)

First, blue may be a primary color, but it’s far from common. The truth is that there just aren’t a lot of blue things in the natural world. Only a few animals are blue, including some birds, insects, and poisonous tree frogs. Chlorophyll and other natural plant pigments are green, red, and yellow, with blue as an occasional modification. Many flowers or fruits that we think of as blue are actually violet, and most truly blue ones are modern creations of breeding and genetics.

To match our environment, our color vision has cones for red and green light that are closer together on the EM spectrum than our blue cones, giving us more sensitivity in the red-to-green range. It seems likely that without modern manmade objects, blue wouldn’t exactly be the first thing on our minds.

That brings us to the related cultural point: you probably don’t need a word for something you don’t have to talk about. Without much blue stuff, maybe you don’t need the word “blue.” Obviously that’s developed over time, but the strong tendency toward red-green in nature isn’t likely to change, so having more blue to talk about mostly relies on the human ability to make blue things.

It’s well known that blue pigments have historically been the hardest and most expensive to make—this was true until about a century ago, and much more so a few thousand years further back. As far as we know, the Egyptians were the first to create blue pigment. Guess who also wins the prize for earliest evidence of a word for blue? (It’s not a trick question. Also the Egyptians.)

Our best guess at present is that the hierarchy of color terms isn’t some deep-seated absolute, but comes from a combination of biological restrictions (environmental colors + our light receptor ranges) and cultural factors (which are affected by a lot of unique circumstances, but also heavily shaped by biology). This is supported by the modeling study, which got accurate results by mimicking human visual limits and leaving the agents alone to work things out in community.

The other major point of contention is what the color term hierarchy actually means. Are people, ancient or modern, without a dedicated word for blue unable to perceive blue the way we do? Do they just have different boundaries for their other colors? (Think of arguing with a friend about whether a certain highlighter color is green or yellow. We all draw slightly different boundaries, even if we see all the same shades.) For the ancient examples, is it possible we’re mistranslating, assuming newer word meanings apply to older writings?

Biologically speaking, ancient Greeks and the people of other early civilizations had the same set of color receptors that we do, so it makes no sense that they’d be blind to the different shades. It’s probably more that they didn’t have practice picking blue out as a separate color category, or maybe even as an important color at all. If you don’t have a reason to look for something, you might look right past it.

“What about the sky?” you ask. Well, what about it? Go out and look, really look at it, and try to imagine that you don’t have the cultural knowledge that the sky is blue. Personally, I can still see it as somewhat blue, but it’s certainly not the same color as most of the other things we call blue. Depending on where you live, it may not be blue most of the time anyway!

More to the point, the color isn’t nearly as important to me in the moment as the feel of the sky. If you weren’t specifically conditioned to compare the color to other blue things, would you think it’s more essential to say the sky is “blue” or to say that it’s “vast” or “clear” or “cloudy” or “deep”?

To me, it doesn’t seem so far-fetched that people might not come up with “blue” based on the sky and water alone. Of course, that’s always the danger with these theories—deciding that something makes sense doesn’t make it true. Without a time machine, we can probably never know for sure what the Greeks, Chinese, Egyptians, or anyone else really meant in their writings.

Luckily, there are aspects of color theory that we can be more certain about, and you can look forward to reading about those soon! Next we’ll approach things more from the physics/biology side.

If you want to check it out, Radiolab has a show on color that will make you think I just copied their list of topics for this set of posts, but I swear I didn’t! I’d done pretty much all my research by the time I found an article that mentioned it. I guess great minds just think alike!