Red means stop, yellow means wait and blue… err what? The colour blue in Japan is used for go but also means green. That’s the traffic signal situation in Japan and it stems back to many years ago. During a time when it was one of the only primary colours used in the light spectrum.
In terms of language, the Japanese word 青 (あお or ao) originally meant blue or green as a shade of blue. In fact, there was no specific word to distinguish the difference. However, in the Heian period, the word 緑 (みどり or midori) was introduced and is now specifically used for green. However, it was and still is considered a shade of blue.
The Introduction of Green
It wasn’t until after the end of World War II that many started to use 緑 (みどり or midori), as it becomes more widespread. From people used it to identify things which specifically reflect that colour.
If we consider the first traffic signal that was introduced in Japan was at Hibiya crossing in 1930. At the time, authorities had decided the official label for the light was 緑色 (みどりいろ or midori iro), which basically means the colour green. Yet, as time went on, people started to refer to the colour of the light as 青 (あお or ao), and so the use of blue name stuck.
Of course, according to international conventions for traffic lights, the official colour is referred to as green. Yet, Japanese traffic lights may seem to have a higher tinge of blue, compared to their foreign counterparts. In addition, if you check the official road rules for Japan they refer to the traffic light now as 青色の灯火 (あおいろのとうか or aoiro no touka), which means blue coloured light.
Other Uses of Blue in Japan
The use of blue to describe more greenish coloured objects isn’t limited to traffic lights either. For example, the use of 青葉 (あおば or aoba) meaning blue leaves, 青芝 (あおしば or aoshiba) referring to blue lawns and 青りんご (あおりんご or aoringo) literally translates into blue apples. All objects which are more like a shade of green rather than blue.
In addition, there is the term 青二才 (あおにさい, lit. “blue 2-year-old”) which means innocent child or child with little experience. There are also two additional related terms 青春 (せいしゅん) and 青年 (せいねん). These both refer to the teenage or youthful years between childhood and coming of age (adult).