Hmm… okay, I’m going to sound a bit nerdy and nitpicky here, but what the heck…
There is no species of cat called Panther. The closest you can come to it is a subspecies of Cougar that lives in Florida, which is called the Florida Panther. But again, this is a subspecies… like the Siberian Tiger or the Asian Lion… A better name really should be the Florida Cougar, but it was called the Florida Panther, and the name stuck. Panther is also used in Florida as another name for the Cougar… the cat with a million names.
Now, Panther is also sometimes used Africa to refer to Leopards… usually when there is a melanistic variation. However, Panther is also used to refer to a meanistic Jaguar as well.
I don’t think that Panthro was modeled after a Black Leopard for two reasons:
One - Black leopard often still have a spots visible. Panthro is uniformly blue… now I’m guessing the liked the blue/grey color better than solid black, but I would hope that they would still show some spots.
Two - Leopards are the smallest of the “Big Cats”… smaller than Cougars even, which are a “Small Cat.” Why would they make the biggest, strongest ThunderCat after the smallest of the Big Cats? And then why use a name that would be confusing to the target audience would would think of Panther in terms of Cougar most likely (North America) or Possible Jaguar (South/Central America)?
I think the simplest answer with regard to Panthro is that the show creators, like many people, genuinely thought that Panther was a separate species of cat, distinct from Jaguar, Leopard, or what have you. Panthro is modeled after this non-existent species of cat.
Merged Post:
Ooohhh… Never even thought of that. Liger could be interesting… very interesting. Of course, this bring up another conversation that I was going to start a some point anyway. Might as well start a new thread now! 
Agreed… There are lots of Medium sized cats that would make for interesting characters based on morphology. Serval with it’s long neck could make for a cool character! 