In virtually every part of the world, traffic light signals are identical: red to stop, yellow to be cautious, and green to proceed.
In Japan, however, some traffic lights switch from green to blue.
In the Japanese language of the past, there were words for only four basic colors: black, white, red, and blue .
Therefore, when describing something green, people would use the closest term to that shade, which is blue.
With the invention of traffic lights, the colors followed international models, but on paper things were different. Official documents described the shades using the classic terms, that is, with "ao" (blue) instead of "midori" (green). Gradually, equipment with variations of these two colors began to appear, and even purple and turquoise appeared in traffic due to this confusion.
In 1973, in an attempt to resolve this problem, the Japanese government decreed that traffic lights should be made with the "bluest possible green" to justify the use of the word "ao" in documents. In this way, they would remain within international standards without compromising their classical language.
So it's actually an extremely bluish green.