Red Light, Blue Light

Some languages refer to colors differently. For instance, Russian and Japanese, have different words for light blue and dark blue, treating them as two distinct colors. Some languages lump colors English speakers see as distinct, together, using the same word for green and blue. 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.
In modern Japanese, ao refers to blue, while the word midori means green. Officially, the “go” color in traffic lights is called ao, even though traffic lights used to be green. This posed a linguistic, the lights are ao in official literature, but they are  really midori.

Since 1973, the Japanese government, in its infinite bureaucratic wisdom has decreed that traffic lights should be green, but that they be the bluest shade of green. They can still qualify as ao, but they are also green enough to mean go to foreigners.