There are different variants of the fish which is a result of extensive cross-breeding program done by hobbyist and fish breeders. Sometimes due to the aggressive breeding techniques matching them with other sub-species, most hybrid mollies don’t even look like one anymore and it can be quite difficult to identify them. Mollies in general are black in color but there are variants which are grayish green to yellow and there is even albino type produced albeit very rare. There are even some with the dorsal that projects like a sailfin although the native molly which you often find has the dorsal fin which is only very short and thin. Nowadays, you can also find a new breed called the “balloon mollies” which has a rounded belly which I believe is part of a selective breeding done by fish breeders.
Molly just like the other livebearer fish which delivers free swimming baby fish also has a gonopodium to insert to the female specimen and the courting affair is usually interesting to watch as the male flaps open and expand its dorsal fin to get the attention of the other fish. The mollies however, do not make good parents as they will eat their own baby fish, and thus once the female delivers the fry, quickly remove it to another tank away from its offspring. To ensure high success rate on getting more fry, you can consider using a breeding box/net or having live plants in the tank so that the baby fish can hide once they are dropped from their mother.