In Japan, green traffic lights are considered “blue” and described as ao shingō (青信号). In modern Japanese although there is a word for “green” (”midori 緑”), which is a relatively new term that has only been used since the Heian Period. Even after “midori” came into use, green was still thought of as a shade of “ao” instead of an independent color and only became distinguished after World War II.
Japanese traffic lights red, yellow, blue? – JapanSugoi – Everything Cool about Japan
Includes a couple other interesting examples of how culture filters even things we take for granted, like the color of the moon.