I didn’t think of that. Could be a mutation if it’s otherwise healthy.Very possible, could also possibly be a mutation as well. It could even be a accidental hybrid to. Personally I never own that specific specie before, I've only ever had Australians and an albino millennium red.
The OP should test their water parameters and post the results to rule out any underlining causes. Personally I'm still leaning towards the maturation process but I could easily be wrong too.
My male has never gotten as dark as the picture from google up above. And he never stays dark, just what he’s showing off for my female rainbow
Is it always like that? Or does it come and go?No damage. If you look closely, it looks like someone has painted the black colour..