Superstitions such as black cats
Often used as symbols of bad luck, black cats grace many Halloween decorations. The black cat's bad reputation dates back to the Dark Ages, when witch hunts were commonplace. Elderly, solitary women were often accused of witchcraft, and their pet cats were said to be their "familiars," or demonic animals that had been given to them by the devil.(Live Science.com)
Medieval folklore also described bats as witches' familiars, and seeing a bat on Halloween was considered to be quite an ominous sign. One myth was that if a bat was spotted flying around one's house three times, it meant that someone in that house would soon die. Another myth was that if a bat flew into your house on Halloween, it was a sign that your house was haunted because ghosts had let the bat in.(Live Science.com)
The traditional Halloween colors of orange and black actually stem from the pagan celebration of autumn and the harvest, with orange symbolizing the colors of the crops and turning leaves, while black marks the "death" of summer and the changing season. Over time, green, purple and yellow have also been introduced into the color scheme of Halloween decorations.