The Tsimane’ people of the Amazon (pronounced chee-MAH-nay, roughly) hunt, farm, and forage. They don’t have a lot of technology. And if you talk to them about the colors they see in the world, they say some pretty interesting things.

For objects that are what an English speaker would probably describe as white, black, or red, the Tsimane’ have specific words too. But show them just about any other color, and their language multiplies. “There’s a huge amount of variability,” says Ted Gibson, a language researcher at MIT who works with the Tsimane’. “Different people would use different terms for what we would call blue and yellow and orange. They really divide up the space differently, depending on the person.”

So, like, Tsimane' speakers who also speak a lot of Spanish say "yushnus" for blue (-ish) and "shandyes" for green (-ish). But others call both the sky and grass "yushnyes," and others call all green and blue things "shandyes." Or, to take another example, different Tsimane' speakers call yellowish colors "cuchicuciyeisi," "ifuyeisi," or "chamus."

In the world of color research, that’s unusual to the point of uniqueness. Across languages and cultures, people tend to break up “colorspace,” the universe of all the colors humans see, in roughly the same way—different words, sure, but for mostly the same colors. So when Gibson told Bevil Conway, a vision researcher at the National Institutes of Health’s Intramural Research Program, about his findings with the Tsimane’, Conway wanted to know more.

Conway studies color and vision; Gibson studies language and information theory, and had been looking at the way Tsimane' speakers use numbers. Together, they cooked up a new research project to figure out how Tsimane’ speakers see what they see—or, more accurately, how they talk about what they see. Because if you accept that all humans with normal vision are capable of seeing the same vast range of colors (which they are) but vary in the way they talk about those colors (which they do), that says something about how they think. Color turns out to be a very good vector for figuring out how the human brain actually works.

The paper that Conway, Gibson, and their colleagues eventually wrote came out in last week’s Proceedings of the National Academies of Science. And the results are … illuminating. Gibson and Conway have a new theory about how the human brain makes color, and it is less about how people see and more about what they do.

In 1969 two UC Berkeley researchers named Brent Berlin and Paul Kay pulled an array of 320 color chips from the thousands that represented the work of Albert Munsell, a Boston artist and teacher who first proposed organizing colors based on hue (the wavelength of the photon), value (brightness), and chroma (saturation, like from pastel to vivid). Berlin and Kay showed their color array to 20 bilingual Bay Area residents, asking them, essentially, to name the colors in their native languages.

For Berlin and Kay, how people used words to describe points in Munsell’s three-dimensional “color space” was a chisel to use against what’s called the Sapir-Whorf hypothesis, an idea from linguistics that basically says language and culture influence what people think. If you don’t have a word for it, you can’t think about it—no word for "green" and you literally cannot see green, to be a reductionist Whorfian about it. So different cultures would necessarily have lots of different color words.

Berlin and Kay didn't buy it. They thought that color-naming was universal, that all languages were on the same path toward complete knowledge of color names, and that the only difference among languages was how far along the path they were.