Black kittens aren't too bad. The hex only lasts for an hour. Ordinary black cats are unlucky for a day at least. If you see a big, black tomcat, battle-scarred from fighting, you could be unlucky for a whole week.
But, never fear, there's a remedy. If you turn counter-clockwise, you can undo the bad luck. So, turn once for a kitten, five times for a cat, fifteen times for a tomcat.
Of course that doesn't work if you go to the zoo and see a black panther. To undo that much bad luck you'd have to turn so many times that you'd be in danger of screwing yourself into the ground and you could disappear completely.