Grue? Bleen? Rellow?
In the previous posting, I mentioned the concept of “grue”, a color that extends to include both shades of green and shades of blue. The term itself is a blend of “green” and “blue” (I personally prefer the term “bleen”, due to my cousin Benny, but linguists and anthropologists tend to use the term “grue”).
What is exactly this “grue”?
Some (better known) languages, such as English, French, Spanish, German, Russian and Japanese, have separate basic color terms for the two “cool primaries” — blue and green. But other languages vary as to their treatments of the cool colors. One popular option is to have the same basic color term to include what counts as shades of blue and as shades of green for us. In other words, “grue” is a so-called composite or disjunctive color category. According to the study by Paul Kay (of the Berlin and Kay 1969 fame) and Luisa Maffi, reported on the WALS website, more than 50% of the languages studied have a basic color term for “grue”. Such languages include Pirahã from the Amazonian jungle, Warlpiri from Australia and Yupik Eskimo.
Other languages with the “grue” term include: Vietnamese xanh, Thai khiaw, Chinese qīng, Korean pureuda, Japanese ao, Yukatek Maya yax, Zulu luhlaza and Old Welsh glas (in Modern Welsh glas came to mean ‘blue’ and gwyrdd means ‘green’).
Other languages entertain other ways of breaking down the cool part of the color space. For instance, languages, spoken as far apart as West Africa, Papua New Guinea and South America, go even further by having a disjunctive basic color category for black-or-green-or-blue. Yet other languages, such as Martu Wangka in Australia and Ifugao in northern Philippines, have the same basic color term covering our shades of green as well as black, but a separate basic color term for green. Another group of languages — including Lele in southern Chad and Javaé in central Brazil — have a disjunctive basic color category for yellow-or-green-or-blue; this possibility of breaking up the color space is particularly interesting because ‘yellow’ is a warm color and ‘green’ and ‘blue’ are cool colors. Even more peculiar is the division of color space into a disjunctive category yellow-or-green and a separate basic color category of blue, which if found (among other languages) in Eastern Cree (in Canada) and Scottish Gaelic (in Scottish Gaelic, gorm means ‘blue’ and uaine means ‘yellow/green’.
Languages also differ with respect to their treatment of the warm primary colors. For example, English and other familiar and not-so-familiar languages — French, German, Spanish, Russian, Japanese, Korean, Mandarin Chinese, Warlpiri and Yupik — have separate basic color terms for ‘yellow’ and ‘red’. Other languages go the disjunctive route on warm primaries, having a composite basic color category of red-or-yellow (or, as I like to call it, “rellow”). Pirahã is one such “rellow” language; in general, “rellow” languages seem to be most common in West Africa and among the native American languages.
Overall, according to Kay and Maffi, there are more “grue” languages than “rellow” languages. In other words, the warm primaries — red and yellow — are much less frequently encoded in a single composite than the cool primaries — green and blue: while Kay and Maffi list 68 languages that have a “grue” term, they list only 15 languages that exercise the “rellow” option. Moreover, no language has been reported that gives separate basic color terms to green and blue while retaining a red-or-yellow composite.
This bias towards distinguishing the warm primaries compared to the cool primaries may have a physical or physiological explanation that involves the anatomy of the human eye. We have three types of color-sensitive cones in the retina of the human eye, corresponding roughly to red, green, and blue sensitive detectors. The “blue” cones are best at detective wavelengths of approximately 425 nm, the “green” cones — 530 mn, and the “red” cones — 565 nm.
However, these numbers are just for peak sensitivity: for example, it doesn’t mean that the “blue” cones absorb photons only at 425 nm. In fact, as can be seen from the diagram above, these cones absorb light at a range of wavelengths, from violet to blue and even some shades of green. But their sensitivity to light decreases as the wevelength moves away from the peak at 425 nm. When green light at 520 mn hits a “blue” cone, a much smaller percentage of photons are absorbed compared to light at 425 nm. The same is true of the “gree” and “red” cones, which too absorb a range of wavelengths. So in a way, each color-sensitive cone is not color sensitive at all! What a cone registers is not the wavelength of light that hits it, but rather the intensity of different wavelengths. That’s why a superimposition of “pure” red light at 620 nm and “pure” green light at 540 nm gives us an impression of yellow!
Notice also that the three types of cones are distributed over the spectrum of wavelengths in an uneven fashion: the peak sensitivities of the “green” and the “red” cones are closer to each other than those of the “blue” and the “green” cones. That is why yellow is perceived on the color spectrum (see below) as the narrowest band of “separate color”.