Hi there wan1967.
In a pet shop there are no different types of mollies. All of the mollies in a typical pet shop are crosses of P. sphenops and other wild type mollies. The color variations are not different fish but merely different characteristics chosen by the commercial breeders. As far as the fish are concerned, they are all the same fish. So-called dalmatian mollies will breed freely with greens, sailfins and black mollies, lyretailed or otherwise. You will not find any pure wild type mollies like P. velifera or P. sphenops in a typical pet shop, ever.
I have noticed that dalmatians do indeed grow darker with age.