Try getting better pictures of each fish. You can't really see much from these photo's. Try taking a closer dorsal picture of each, as well as pictures showing the sides of each fish, to better get a look at the shape of the fish and the odontodale growth. & try to take a picture through glass or clear plastic as to avoid any distortion. (see how some of the gravel isn't very clear due to the water movement on the surface, that makes it even harder to see odontodals in your picture)
they are either both male or the darker one is female and the lighter one is male just based off of odonotes on the pectoral alone. according to Amazonas magazine which had a breeding article on these, the odonotes on the pectorals is one of the most surefire ways of telling them apart. but as we can see the fish in your photos are not completely mature yet, so it is hard to tell until they grow their odonotes longer.