The dark color in the dorsal usually indicates female in Nandopsis.
And although yours has developed a more male profile, this is common if a male of that species is not present, and commonly happens that the female may adopt dominant traits.
I had a female Nandopsis haitiensus whose profile and coloration would change to a more male look, over night if the male was removed from the tank.
normally she looked like this
![](/forums/proxy.php?image=http%3A%2F%2Fi70.photobucket.com%2Falbums%2Fi97%2Fdstuer%2FHaitiensis%2Ffemale%2520hait%2Fhaits10012.jpg&hash=7762bee6873a4b84ba6ccac78c9e6b53)
but if the male was removed, she became this
![](/forums/proxy.php?image=http%3A%2F%2Fi70.photobucket.com%2Falbums%2Fi97%2Fdstuer%2FHaitiensis%2Ffemale%2520hait%2FSat19012.jpg&hash=e3c1085f7d23f7b0a0d4dc3871122bb9)
below is a normal female Nandopsis tetracanthus (Cuban) note the dark color in the anterior of the dorsal
![](/forums/proxy.php?image=http%3A%2F%2Fi70.photobucket.com%2Falbums%2Fi97%2Fdstuer%2Fcubanos%2Fpipetting2008.jpg&hash=e1cb01ec1ee82e4d88679911b39a0ec5)
below the male