Yes, the recessive gene may make it possible I suppose. Thing is, to make that possible, there would have to have been, more melanistics released, than normal coloured Leopards, back in the day, and I don't think there is much, or any evidence of that. If there is evidence of such, I'm sure greyman would have that information.
Without any proof, we can only go on hearsay, and hearsay never proved anything.