1. blue; azure
だが、いったい青がそんなに冷たい色なのか？But is blue really such a cold color?
2. green
mostly in compound words and in ref. to fruits, plants and traffic lights
この信号、なかなか青にならないね。This light is taking forever to turn green, isn't it?
3. green light (traffic)
そして、信号が青になる。And then, the traffic light turns green.
4. black (horse coat color)
5. blue 5-point card
6. immature; unripe; young