[phoenixhieghts]

I have 2 anthias.
When i first made the purchase it was as a female and male.
I noticed both were as orange as each other, and the male had an elongated dorsal fin.
But as time has gone by the male has gone so much darker, almost to the point of having a black colouration to him.

But in your case i would not worry. Anthias are hermethrodites (spelling :s), they may have been a mated pair but then the female may have decided to become a male.
Elongated Dorsal fins are only with males.