Basically, this is when the main outfit of a redhead, auburn, or even a pink-haired character is (at least mostly) green. This trope can sometimes be used to hint that somebody is of Irish descent, but sometimes, illustrators use it for traditional Red/Green Contrast or because they just feel like it. Bonus points if the character in question has nature-themed abilities.
RedHead in Green has been suggested to play 3 roles. Click below to see other actors suggested for each role, and vote for who you think would play the role best.