Most people believe that black cats signal bad luck if you happen to come across them. This superstition is a big reason that a majority of black cats in animal shelters don't get adopted as frequently as other types.
In the Middle Ages, black cats became associated with black magic and the devil. Pope Gregory XI claimed that Satan could take the form of a black cat when walking the earth. The result was panic and slaughter of thousands of black cats over the following century. During the times of American colonization, black felines became associated with evil and witchcraft. This belief is also perpetrated in the media such as Sabrina the Teenage Witch owning a black cat named Salem. The association with witchcraft is also how the myth that cats have nine lives began. It was rumored that a witch had the ability to shape-shift into a cat nine times.
Because of the number of black cats in animal shelters, some have held events such as "Adopt Your Own Panther" in Nevada to make owning a black cat more appealing. Many black cats also come with lower adoption fees as well. Another reason that black cats seem to get adopted less, is sometimes their fur does not do well for photography and nowadays many people look for adoptable pets online and a bad picture or none at all can make a big difference.
Unfortunately, Halloween, which is just in two weeks, has also been a time when some people acquire pets—particularly cats —to use as living decorations or for displays of fun and sport, only to discard or abandon them afterward (as often happens with chicks and rabbits at Easter time). Accordingly, many animal shelters have taken steps in recent years to limit or eliminate the adoption of cats in the days leading up to Halloween by either deferring feline adoptions until after Halloween or by more carefully scrutinizing the prospective adopters.
While I instantly fell in love with my Siamese mix cat, Ollie, the next day my family went back and got our black cat, Cyrus. My younger cousin wanted a cat after I brought mine home and both are wonderful pets and absolutely love to hang out and play together.