What is the origin of the idiom "green with envy" and when to use it?

The phrase "green with envy" has its roots in ancient Greek and Roman mythology. In these cultures, green was associated with sickness and the pale pallor of a person's face when they were ill. Over time, the association of green with sickness evolved into symbolizing envy or jealousy. It is used to describe someone who is extremely jealous or envious of another person's possessions, achievements, or qualities. It suggests that the person's envy is so intense that it figuratively turns their complexion green, emphasizing the depth of their jealousy.