Contrary to popular belief, black cats have not always meant bad luck or been associated with witches. In fact, the oldest traditions have black cats as bringers of good luck and white cats being the creepy ones. Having known several white cats, I can see where that one comes from! A white cat can look so unearthly sometimes. Anyway, I thought it was interesting that this Victorian greeting from The Graphics Fairy refers to black cats as being lucky.
Wouldn't it be fun to print it out and send it as a card to all of your friends for Halloween? If you mail it soon, it should get there in time!