Paracheilinus cyaneus is similar to P. nursalim, but differs most notably in having a magenta or reddish ground colour compared to the predominately orange colour of P. nursalim; in having a yellowish brown triangular marking on the spinous dorsal fin, red dorsal and ventral margins on the caudal fin which extend onto the filamentous lobes, and possession of a blue band below the eye that is about twice the width of that present in P. nursalim; lacks the pair of prominent blackish patches present in P. nursalim below the anterior dorsal fin and ventral half of the caudal peduncle. In P. nursalim either one or both of the filamentous caudal-fin lobes are generally longer than those of P. yaneus, reaching about 50% of the standard length in some individuals. P. cyaneus has a strong turquoise hue over the head, adjacent anterior body, and along the back, extending onto the dorsal fin during the climax of courtship display (Ref. 74967).