Pantherid melanism

I was reading Rudyard Kipling's "The Spring Running" this morning, and I've been thingking of Bagheera, the black panther, ever since. My fancy for pantherids was once again aflame. Thus, I did some research on cases of melanism in the genus Panthera (leo, tigris, onca, and pardus; the lion, tiger, jaguar, and leopard, respectively).
According to what I have read, melanism in the species P. pardus is most profound in the the South East Asian population, where black panthers are more common than normally colored individuals. Also, melanistic leopards are on average smaller and more lightly built than their yellowish counterparts.
Regarding P. onca, I believe the distribution of panthers and normal jaguars is even, though the panther gene is dominant. Unlike the black leopards though, the native South Americans (I don not know if this is factual, however) claim that black specimens are larger and more aggressive. This I can not explain, but the distribution of black and normal individuals (in both onca and pardus) is a simple matter of habitat.
I have every reason to believe that leopards in SE Asia more commonly habituate dense rainforests, where the canopy blocks out most of the sunlight. This is a prime example of evolution taking place due to specific requirements. In such a dark place as that, a black coat is much more preferable than a yellowish one.
The said reason is similar for P. onca, and the even distribution of blacks and normals is probably due to South America's relatively irregular forest pattern.

As for the two remaining species...

I have only read of a single account of a black lion. This was a report of a very big Persian lion that was seen by the archaeologist Sir Henry Layard which was described as being "very dark brown in colour, in parts almost black." There are, of course, no lions at all left in Persia today...much less big black ones. There are two explanations for this specimen's existence: one is melanism. The other is that the darkness of a lion's mane and possible its coat is affected by climate. Lions in Europe are darker than lions in Africa (this is because of Europe's colder climate).
There are, however, leucistic specimens of P. tigrs and P. leo (there are also reports of white jaguars, and white leopards have been discovered, but these are very rare). These individuals, though, are not products of evolution. They are actually random mutants, though their coats might help in their grassy habitat.