6.4. What colour is ao?

The colour ao (青) is a confusing one, since not only are blue skies said to be aozora (青空), but green traffic lights are also ao.

According to Gendai Kokugo Reikai Jiten published by Shogakukan, ao is the Japanese name for the printing ink colour "cyan", and it is used for both green and for sky blue and sea blue.

The Koujien dictionary's entry also says that ao is the name of sky blue, sea blue and green. It also explains that according to one historical explanation, in ancient Japan the only colours were aka, shiro, kuro and ao. This dictionary also notes that historically aoi meant a medatanu iro, a "dull colour", and was used even for grey. It now covers colours as far apart as ai, a dark blue, midori, green, and sou, the colour of grass.