“What shows up in the new fry that would prove something about the species?”
Vigour, vital energy. No colours, no special information about a species, but the fact that they live and thrive, prosper. Hybrids (in most cases) if they ever leave their eggs are often weak, don’t feed, die soon. There maybe close hybrids of course that do well, but normally they don’t. We know very little about this for Parosphromenus, however.