The image of the black-coated, red-maned alicorn is an old and powerful one, synonymous with treachery, narcissism, and being kind of a ponce overall.

On Nightmare Night it is said that, during Discord's reign, Equestria was nearly saved by such an alicorn, wielding amazing powers, only for said alicorn to demonstrate a really big superiority complex and basically lord it over everypony else. After a year or so of constant petty annoyances, this alicorn was overthrown (to great applause) by a group of commoners led by what turned out to be Discord wearing a skirt. (This sort of thing was actually fairly standard for the time period, but for whatever reason, this particular event wedged itself firmly into pony folklore and wouldn't leave.)

Certain books in the dustier sections of the Canterlot archives, if perused for information on said alicorn, would mention several unconfirmed sightings of this alicorn throughout history. Every one of these sightings, however, allegedly ended similarly to the original event in the Age of Chaos, insofar that the alicorn in question apparently was incredibly annoying and eventually disappeared without a trace.

Ebony Redwood, the Ponyville mare living in the house with the bluish shingles, has heard the legends many times, and doesn't much care for them. Most ponies assume she's simply tired of all the unfair prejudice leveled against her just because her colors make her look kind of like a B-list superstition, and they'd be right.

Four thousand years is enough time to get tired of hearing things you like, after all.