When it's all said and done and speculated on, there are endless citations that state that no totally black wild Puma concolor aberrant has ever been collected in any of its range worldwide - from far north in North America to far south in South America. That's the only way to confirm whether these aberrations do in fact exist in this species. An aberrant black jaguar or leopard might be possible that has escaped from somebody, but not a native cougar. So I will rate so called black panther sightings here along the same lines as Bigfoot sightings until somebody actually captures or kills one. Just people just seeing what they want to see, often for public notoriety (with Bigfoot anyway).
FWIW, the species Puma (Felis) concolor is now considered to have only 6 subspecies worldwide (in North, Central & South America), none of which are known to produce all black aberrants. Over two dozen old ssp names are no longer considered valid in the world of taxonomy due to more advanced DNA methods that determined they were invalid subspecies. But the world is slow to catch on, so many old ssp names are still referred to, including for the so called Florida Panther (was listed as ssp coyri). Regardless, only one of those 6 ssp are found in the United States, so all lions found in this country "naturally" should be Puma concolor cougar, including those in Florida and those along our southern borders to Mexico. Thee next closest ssp to our borders ranges naturally from Nicaragua to Panama.
