Have you ever stopped to think – all the characters in Harry Potter are stereotypical magic users, as we muggles think of them?
Hermione's bushy hair, McGonagall's pointed hat and feline alter ego, and Dumbledore's twinkling eyes, long beard, and star and moon robes, are just the more obvious examples. You've got Snape, hooked nose, sallow, greasy black hair, yep he's a stereotype. The abundance of red-haired wizards and witches – not just the Weasleys, either - check. Talk about stereotypical coloring for magic types – black hair and green eyes? That's really popular.
Hooch, Luna Lovegood, Gilderoy Lockhart, Pomona Sprout, Lucius Malfoy with his cane: the list goes on. They all have at least some trait that we as a fandom recognizes and identifies as witchy, even before we knew these particular characters so well.
There's just one glaring exception, to me. Why is there no witch or wizard with green skin and an allergy to water? This plot has festered and grown in my head for several years now, due to this concept. I have an outline. If there is any interest, I'll go ahead and actually write the story.