Road traffic in Japan is a complicated affair. Apart from those narrow, crooked streets that sometimes end without warning, you have to get used to unclear right-of-way rules and the national fetish for backward parking. On top of that they drive on the wrong side of the road (though admittedly views may differ on that).

What can really give you the blues, however, is what they call their green traffic lights. Whereas 赤 (あか, red) and 黄 (き, yellow) basically go by the same name as everywhere else, the Japanese green light is not called 緑 (みどり), the Japanese word for green, but 青 (あお, blue).

To be sure about one thing, though some traffic lights in Japan may in fact look just a little bluer than elsewhere — we’ll come to that in a minute — all of them are clearly within the physical spectrum defined as green. That’s because the colors of traffic lights are subject to an international convention according to which the “go” signal must be green. No exceptions granted.

In order to find out how the matter is dealt with in official documents, I consulted the “Traffic Safety Guidelines for Pedestrians and Cyclists 歩行者と自転車のための日本における交通安全ガイド,” a recent bilingual publication by the National Police Agency. Here the English text specifies that the “green light” indicates that “pedestrians can proceed to cross the street.” In the accompanying Japanese text, by contrast, this very rule applies to 青色の灯火 (あおいろのとうか, the blue-colored light). By the way, both texts refer to the same illustration, the image of a traffic light in red, yellow and, well, something turquoise.

At the heart of the confusion is the rather puzzling nature of the word 青 itself. In fact, it’s not only the “go” color of traffic lights that is referred to by this word, but a couple of other things too that would appear rather unblue. Thus we have 青葉 (あおば, blue leaves), 青芝 (あおしば, blue lawns) and 青りんご (blue apples), not to forget that well-known Tokyo upper-class district called 青山 (あおやま, blue mountain). In addition, there is the term 青二才 (あおにさい, lit. “blue 2-year-old”) to refer to inexperienced youths and other greenhorns. Speaking of which, we must not forget the two terms 青春 (せいしゅん) and 青年 (せいねん), both of which denote the somewhat unripe years between childhood and coming of age.

As becomes obvious here, the color term 青 comprises quite a few things and concepts that in English (and many other languages) are normally associated with the color green. The most common explanation for this is that the word 青 originally comprised both blue and green. This “grue” category, as it is called in color nomenclature research, has been identified for a couple of other languages as well. In Japan, it was only after the term 緑 came into usage that the color spectrum referred to by 青 narrowed from “grue” to blue. As a result, today most things that are green are in fact referred to as 緑. Exceptions such as the odd blue lawn or leaf are but relics from the old “grue” days.

But what about the traffic lights, which inarguably must have arrived on the archipelago quite some time after the blue-green split? According to official records, the first traffic light in Japan was set up at Hibiya Crossing in 1930. Quite surprisingly, the “go” color was officially referred to as 緑色 (みどりいろ) then. However, as traffic lights became a more common sight throughout the country, people started to speak of 青 rather than 緑. Apart from the long shadow of the former “grue” category, this was most likely due to the fact that red, blue and yellow (赤青黄) are regarded as the three primary colors in Japanese painting. Hence the “blue” traffic lights.

But this is not yet the end of the story. According to the late Francis Conlan, an Australia-based linguist who dedicated a dissertation over 500 pages long to the little word 青, the government apparently saw some need to get the name and the color of the “go” light closer together again. As they didn’t want to change the common practice of calling it 青, however, in 1973 a decree was issued according to which the “go” light should be changed to the bluest possible hue of green. This would make it factually bluer without having to change the name from 青 to 緑.

The result is the present state of affairs: a mixture of more or less bluish green lights that the local population calls 青, while to most non-Japanese eyes they look (almost) as green as everywhere else on this planet. No matter how hard you try to see them blue.