El Gato Negro ... and Ligers?
It may be when they say there are no "black pumas" they speak as an artist who knows what the color true black is. When there were many pumas roaming the US, dark brown and slate grey pumas were apparently confirmed, and black pumas widely reported.
Over at MessyBeast they seem quite fascinated in mutant cats, cross breeds, and the related genetics.
The "Cherokee Cougar" taxidermy is claimed to be a black puma [..] DNA testing by East Tennessee State University's Zoology Dept appears to confirm it as a puma and that hairs tested were not dyed, however there are no definitive results confirming it as a melanistic individual [..] the black puma taxidermy may be a recessive mutation.
Then again, the site devotes thought to Liger and Tigons, and much of the data mentioned seems anecdotal and well aged.
So to clarify, there is no such thing as a big black cat in California, there are no black mountain lions. Unless you see one.
If you see one and bring it home, you may, with the help of skeptical scientists, prove they exist.