In one of my tanks I do keep Poecilia salvatoris (wild molly) and Xiphophorus helleri Rio papaloapan (wild swordtail) together. Some El silverado endlers are swimming in there as well. This combo works really well. What I like about the P.salvatoris is that the body is plain in coloration but the fins (especially the males) have red, black and white in there. The females have mainly red in their fins. They're slender build mollies in comparison to the mollies most people know.
Above: Male P.salvatoris
Above: Female P.salvatoris
Above: P.salvatoris, male (bottom) & female (top)
Below: A bunch of these P.salvatoris
Below: A combo of Rio papaloapan swordtails and Poecilia salvatoris
Below: A bunch of Rio papaloapan swordtails
Above: Male P.salvatoris
Above: Female P.salvatoris
Above: P.salvatoris, male (bottom) & female (top)
Below: A bunch of these P.salvatoris
Below: A combo of Rio papaloapan swordtails and Poecilia salvatoris
Below: A bunch of Rio papaloapan swordtails