Traffic lights – Butch

Why Japanese people say “blue signal” instead of “green signal” in traffic light. As everyone knows, it’s obviously blue coloured signal. Why can’t people say “blue”?? On law until 1946, a "green signal" is right and does not call it a blue signal. However from Japanese sensibility, we tend to call “blue” instead of “green” in many things. For instance, “Seika which means blue and fruits in Japanese” for “green vegetable”, moreover, “Aoba which means blue and leaves in Japanese” for “green leaves”. In the law by the legal revision in 1947, “blue signal (Aosingo in Japanese)” is right to call it. In spite of that, traffic lights still have green colours. I always wonder that!