I know that both leopards and jaguars have the occasional “melanisitic” individual, that people refer to as a “black panther”. Do any other big cats have this variation? Are there “black lions” or “black tigers”? How about “black pumas/cougars” – or any other wild cats, big or small?
Melanism is a relatively common mutation; I’ve seen it in many different animals. Somewhere I have some pictures I took a few years ago of a melanistic mallard: jet black duck with an iridescent palimpsest of purple, bronze, and green. Breathtaking.
“Palimpsest” - not a word you hear every day, and an interesting alternative to “watermark” which is also a fair way to describe the show-through of the normal colour pattern. 
While I’m sure the odd non jaguar or leopard has this, I suspect they have this crop up more commonly because it’s not a significant drain on their hunting ability, or it may even be an occaisional advantage.