The color blue may be the most confusing word in the Japanese language.

The go-signal on traffic lights in Japan is blue. But they're really green. What I mean is that while the actual color of the go-light is green, as it is in every country, it's called blue in Japanese (ao, 青).

A long time ago, there was no separate word for green color in Japanese. Instead, green was grouped with blue, and that linguistic artifact got stuck on traffic lights.

Below is a pedestrian safety poster with a red-and-blue traffic light and a photo of a traffic signal in Japan.