If we translate the name of a traffic light from Japanese, we get the phrase "blue signal. But nowhere in the streets of Japanese cities do you see blue traffic lights - their color will be absolutely standard and customary: red, yellow, green.
What is the reason for this confusion? Look for it in history. On 8th November 1968, most countries of the world adopted the Vienna Convention on Road Signs and Signals, which led to an international standardization of these signs. Japan, however, decided to go its own way and introduced a blue permit signal instead of a green one. Five years later, however, the Japanese government changed its mind and installed a green permit signal. This step was due to the poor visibility of the blue signal over long distances: the corresponding blue electromagnetic waves are well scattered in the atmosphere.
However, even the residents of the Land of the Rising Sun continued to call the green traffic light "ao shingu" - "blue signal. This is due to a feature of Japanese culture, where it has long been customary to consider green as one of the shades of blue.
The character pronounced "ao" denotes the reference color blue, but its shades of light, dark, or going green are also denoted by the same character in certain contexts. Thus the green-blue traffic light has become one of the symbols of the complexity and confusion of the Japanese language and culture.