The peculiar case of 青い (あおい)

青い (あおい) as a colour is something that is difficult to understand for some. In itself nowadays it represents the colour azure, which is the blue colour of the sky on a sunny cloudless day. If you’d have to translate it as one primary colour, you would also say blue. But due to historical reasons in daily life 青い (あおい) sometimes is used to refer to multiple colours, namely blue, purple, gray, green and pale. That’s why Japanese refer to the green stop light with 青い (あおい), even though Japanese also has a word for green: 緑 (みどり). Crazy right? In real life 青い (あおい) has some specific meanings which are outlined below.

青い (あおい) means blue when used for

• Almost all things that are painted blue (blue car, blue house, blue shirt)
• The sky
• The water
• Eyes

Examples:

青い (あおい) means green when used for

• Fruit, like an apple: A green apple for example would be called 青りんご (あおりんご). Technically this would mean blue apple, even though you are looking at a green one. Here is a link to Google Images to show you what I mean.
• Vegetables: All kind of vegetables and eatable plants that have green foliage are referred to as 青い野菜 (あおいやさい). This also holds for grass and crops
• The stop light: Strangely enough, specifically the green traffic light is referred to as 青い. When you use 緑 (みどり), this will sound very strange.
  

  	信号が青になったよ
  	しんごうがあおいになったよ
  	The traffic light turned green
  	しんごう	信号	Traffic light

青い (あおい) for grey objects and beings

• Grey Heron, a large bird found all over Africa, Europe and Asia. You probably know the gray heron in your own language under a completely different name, so here is a link to Wikipedia to show what I mean. The bird is obviously grey but in Japanese it’s called アオサギ (aosagi)

青い (あおい) in proverbs

青い is used in some older proverbs that have a more or less similar meaning in English. For example, it is used to indicate someone who is young or inexperienced.