Witches are typically depicted with green skin in pop culture, like their research into the occult arts has resulted in some sort of strange mossy skin condition.
Most of the time it adds to their creepiness, and makes them the perfect social outcasts, embittered and hell bent on revenge, but where did this tradition of greenification come from?
Linda Rodriguez McRobbie at Boing Boing explored the origins of the green witch and came up with one fairly obvious root cause- the Wizard of Oz.
The 1939 film changed the face of pop culture, and ever since Margaret Hamilton's Wicked Witch of the West was shown sporting skin a glorious shade of Technicolor green the color has become a witchy standard.