Black cats have been considered symbols of both bad luck and good luck for hundreds of years. In colonial New England, black cats were often considered "familiars" of witches, or, spiritual guides that helped witches commit evil. Others believed that black cats were witches themselves who had shape-shifted.  Black cats that walked across the paths of people were thought to be omens of misfortune. In the United States, black cats are common symbols of Halloween.  

Some people still consider black cats symbols of bad luck. In fact, black cats are adopted from shelters less often than other kinds of cats. To combat superstitions about black cats, the United States, England, and Ireland each have black cat appreciation or protection days built into their calendars. 

Conversely, black cats that wandered into people's homes in Scotland signified prosperity. Fishermen's wives sometimes kept black cats at home because they thought that keeping such a cat might help their husbands remain safe on the high seas. 

Despite the many superstitions attached to black cats, they are quite common and are really just ordinary house cats. There are 22 kinds of cats that can have black coats. Such cats may have completely black coats, or, coats that "rust," or turn slightly reddish or brownish from sun exposure. Some black cats can "gray" over time like humans! Most black cats have yellow or green eyes.