Black Cat Appreciation Day was created by animal shelters to celebrate the awesome mini-panthers you can share your home with. Partially because of silly superstitions about them being bad luck black cats are the least likely to get adopted and therefore the most likely to get euthanized simply for the color of their coat.
I personally live with 2 black cats (photo is my baby girl Pumpkin) and I assure you they will not bring you bad luck. If you are looking for a new friend please consider the sleek, wonderful black cat at your local shelter.