mysterybox,
Thank you for your patience. Your new Halichoeres melanurus looks beautiful, and hopefully the fish is settling in well into your aquarium.
Labrids of the genus Halichoeres are protogynous hermaphrodites, and at maturity, these fishes will display initial phase (both males and females) or terminal phase (males resulting from a female sex change) coloration and patterns.
Your new fish is still in the Initial Phase, and the exact sex is very hard to determine. When this species starts changing sex from female to male, the horizontal striped pattern and coloration on the head and face of the fish will gradually start to change to thicker stripes, with a distinct yellow/lime green patch on the upper region of the operculum, and yellow patch or spot at the base of each pectoral fin. During this transformation the fish will also lose the three black spots along the dorsal fin, changing from spots to thick stripes, and the tail will also develop coloration and pattern, going from clear to a blue, red/orange, and green with black vertical band at the outermost part.
I hope you find this information beneficial, and I hope you enjoy your new Halichoeres wrasse.
Cheers!