Wrasse Identification

[naesco]

You don't have a pic but I looked at Kuiters book.
The difference between the male and female is that the males have a black margin on the dorsal fin and a white line along the base of the fin.
If the fin is all black it is not what they say it is.
Having said that, as you may know I read that sometimes these fish interbreed so it may be a half and half fairy wrasse.