It is our feeling that the red color morph may well be another subspecies. Color and pattern can vary with geographic origin. A broad pale edged dark reddish brown stripe extends from the snout, through the eye, to the neck. The head is also dark reddish brown in color with paler patterns matching the body's ground color. Males have a larger head than females and the female heads are also narrower and more pointed.
Eye color ranges from red to orange with black pupils.
It is our feeling that eye color can be used as an indicator of an animals sex with males having a more fiery red color than females. The tail is ringed with backwardly projecting spines which are blunt to the touch but used to wedge themselves in rock crevices or other cavities making it difficult to pull them out. We have read of reports indicating the tail is used as a club or a whip, but have never witnessed this behavior. The tail is dark brown with indistinct rings matching the body ground color. Unlike many monitor species, acanthurus get more beautiful and colorful with age.