Blue is a cool color. The traditional Blues Music in the United States is the opposite of Red Hot Music.
Blues is slow, sad, and sorrowful. Duke Ellington and his orchestra recorded a famous song Mood Indigo about the deep blue color indigo.
In the words of the song, “You ain't been blue, till you've had that Mood Indigo.” Someone who is blue is very sad.
The color green is natural for trees and grass. But it is an unnatural color for humans.
A person who has a sick feeling stomach may say she feels a little green.
A passenger on a boat who is feeling very sick from high waves may look very green.
Sometimes a person may be upset because he does not have something as nice as a friend has, like a fast new car, that person may say he is green with envy.
Some people are green with envy because a friend has more dollars or greenbacks.
