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Trope: Significant Green Eyed Red Head
Description: What it says. ;) Okay, okay, I know this is a pretty minor trope, but it's timely, so bear with me. As red and green are opposite each other on the color wheel, combinations of them are a quick way of calling attention to an important character. There tend to be more women then men fitting this trope, and the combination of red hair and green eyes is frequently thought to be alluring.
Examples: Jessica Rabbit, Poison Ivy, Mary Jane from Spiderman
Pros: As noted above, the bright, complimentary colors are ways to draw attention to a character. Redheads themselves have a slew of associated tropes, and just the simple act of giving a character red hair can have certain connotations and give the audience an idea of what to expect.
Cons: Natural redheads with naturally green eyes don't pop up all that often in nature, despite what creators of art might have you think. Also, as stated in the "pros" list, there are a number of closely-related tropes, and some of them have been done to death. (How many "feisty" redheads are there in books/movies/TV shows/comics/etc.?)
Would/Did I Use It?: Guilty as charged, though I admit I stumbled into this one blindly. Tanith, one of the antagonists in Disintegration (and star of her own mini-prequel), has green eyes and flaming red hair. I honestly didn't know about this trope before I described her in this way; however, I will confess to loosely basing her physical appearance off of Aveline from Dragon Age 2. (Whether or not you consider Aveline significant is another story...I think there are far more significant characters in the game, but mileage varies!)