Ao (color)
Ao (hiragana あお; kanji 青; adjective form aoi (青い). is a Japanese color word that includes what English-speakers would call blue and green. For example, in Japan, blue skies are described as aozora (青空), and green traffic lights are described as ao-shingō (青信号).
Ao versus midori
Modern Japanese has a separate word for green, midori (緑), although its boundaries are not the same as in English. Ancient Japanese did not have this distinction: the word midori only came into use in the Heian period, and at that time (and for a long time thereafter) midori was still considered a shade of ao. Educational materials distinguishing green and blue only came into use after World War II, during the Occupation: thus, even though most Japanese consider them to be green, the word ao is still used to describe certain vegetables, apples and vegetation. Ao is also the name for the color of a traffic light, "green" in English. However, most other objects—a green car, a green sweater, and so forth—will generally be called midori. Japanese people also sometimes use the English loanword gurīn (グリーン) for colors. The language also has several other words meaning specific shades of green and blue.