Molly Appearance and Behavior. In the wild, the common molly exhibits a dull, silvery color. While their bodies tend to be light gray in color, mating males may exhibit more of a greenish-blue color. The sides, backs and dorsal fins of many mollies are dotted with rows of spots.
In some types, male fins are pointy on the ends, and their tail has more angled edges. Fancy molly fish types have long, flowing fins on males, and females have shorter fancy fins that are held close to their bodies but not clamped. You can also tell the molly fish male and female by comparing their coloring.
Black mollies (the most common molly fish type) have all-black bodies and rounded fins between three and six inches long. Sailfin mollies have light gray bodies with rows of dark gray spots and an enlarged dorsal fin that looks like a boat sail.