I don't know anything about Japanese, but if "aoi" is used to describe both the sky and unripe fruit, what makes linguists say that the correct translation for "aoi" is blue? Wouldn't it make more sense to say that "aoi" means "green/blue", i.e. a general term for both green and blue? Doesn't it make the relationship between the words "aoi" and "midori" the same as the relationship between the words "rectangle" and "square" - one is a superset of the other?