Genicanthus melanospilos shows sexual dichromatism, the males and females have differing colouration. The males have a background colour of bluish white on the body with many reddish black vertical stripes. Their dorsal, caudal and anal fins are marked with yellow spots and the caudal fin is light yellow with blue margins and has long filamentous lobes. They also have a sizeable black spot on the breast near the base of the pelvic fins.^[3] In the females the dorsal half of the body is yellow, while ventrally it is bluish white, and the tail is bluish with a black stripe along its lower and upper margins. In both sexes the forked tail narrows at its base to create a “swallow tail”.^[4] The dorsal fin contains 15 spines and 15-17 soft rays while the anal fin has 3 spines and 17-18 soft rays. This species attains a maximum total length of 18 centimetres (7.1 in).^[2]