Green with envy

Green with envy = jaloux comme un pou

In many Western cultures the feelings of envy or jealousy are commonly associated with the color green. A greenish facial tint has long been associated with illness, as suggested by the phrase "green around the gills. (avoir mauvaise mine)" As a person who is very envious is considered by many folks to be unwell, these people have been described as "green (or sick) with envy." 

Long before Shakespeare connected green with jealousy, the color was more commonly used to describe illness. The early Greeks interchanged "green" and "pale" to mean sickly. The Greeks thought that when you were ill or jealous, the body produced too much bile, giving the skin a green tint.