Green is an important color in nature . It is the color of grass and the leaves on trees . It is also the color of most growing plants . Sometimes , the word “ green ” means young , fresh and growing . For example , a greenborn is someone who has no experience . In the 15 th century , a greenborn was a young cow or an ox whose borns (角) had not yet developed . A century later , a greenborn was a soldier who had no experience in war . By the 18 th century , a greenborn had the meaning it has today - a person who is new in a job . Someone who is good at growing plants is said to have a green thumb (大拇指). The expression comes from the early 20 th century . A person with a green thumb can make plants grow quickly and well . The Green Revolution (绿色革命) is t he name given some years ago to the development of new kinds of rice and other grains . It was the result of hard work by agricultural scientists who had green thumbs . Green is also the color used to describe the powerful feeling . Jealousy (嫉妒). The green eyed monster is not a dangerous animal from outer space . It is an expression used about 400 years ago by the British writer William Shakespeare in his play “ Othello ” . It describes the unpleasant feeling when someone has something he wants . In most places in the world , a green light is a signal (信号) to move ahead . In everyday speech , a green light means approval (赞成) to continue with a project .