Green is an important colour. But "green" is more than just a colour. It is the colour of grass and leaves. It is also the colour of most growing plants（植物）.
Sometimes, the word "green" means young and growing. It is something that is not ripe（成熟）. A cow has no horn（角）. It is green. "A green hand" means you come to a new job（工作）.
Sometimes, the word "green" means good. The meaning of "a green thumb（拇指）" is that you may have a magic way to make plants grow quickly and well.
Green has another wonderful meaning. You often take a bus to go out, but not take a car. We say you are going green. Because you love the world in a better way.
