In Japan, the “green lights” are colored … well, pretty much blue. The reason has to do with a challenge to the idea that language about so many things — in this case, color differentiation — is some sort of universal constant.
Different languages refer to colors very differently. For instance, some languages, like Russian and Japanese, have different words for light blue and dark blue, treating them as two distinct colors. And some languages lump colors English speakers see as distinct together under the same umbrella, using the same word for green and blue, for instance. Again, Japanese is one of those languages. While there are now separate terms for blue and green, in Old Japanese, the word ao was used for both colors—what English-speaking scholars label grue.
The result? Though Japan adheres to international standards for green traffic signals, they use a very bluish shade of green in the signals themselves, to align with their own linguistic heritage.
Do you want to know more? Why Does Japan Have Blue Traffic Lights Instead of Green? | Mental Floss