The green traffic light is called "blue".

According to the book, Japan From A to Z: Mysteries of Everyday Life Explained by James and Michiko Vardaman, the first traffic signals in Japan were blue instead of green, but the blue lights were difficult to see from a long distance away so they were replaced with green ones. Vardaman says that the custom of referring to traffic lights is a holdover from those days. This sounds like a good explanation, but the problem with it is that you will hear Japanese people refer to other green things (like cucumbers, spinach, and sometimes grass) as being blue as well. This is because historically, Japanese people considered green to be a shade of blue. For example, the Chinese character for blue, pronounced ao is made up of two characters, iki (life) and i (well) and refers to the colour of plants which grow around a well, a colour between green and blue. When Chinese people see the character, they say it means green, but Japanese people say it means blue. Japanese books on colours tell us that there are four tertiary colours: red, blue, white and black, and that all others are shades of those four main ones. Ao, therefore, is a sort of ideal blue, halfway between green and blue. The sky is said to be blue, but it is a different shade of ao than a traffic light is. Tree leaves are said to be green, but green is a shade of ao, like crimson is a shade of red. In another interesting cultural difference relating to colour, Japanese children always colour the sun red instead of yellow.link