The only exception was when he briefly wore a light-colored Chinese battle costume at the start of the Dark Tournament. He is the only one of the four main characters to never change his primary 'costume' during the series. He wears a black (and sometimes pale blue) undershirt under the jacket. He wears a long black cloak-like jacket (with a white collar) and black pants tucked into black boots.
Living up to his classic villainous persona, he usually dresses entirely in black. His skin complexion is regular peach-tan. He has spiky black hair (reminiscent of Vegeta from the Dragon Ball franchise) with blue outlining and white streaks. His eyes are crimson (blood red), with an angular and slightly slanted shape, giving him a very sinister look in the beginning of the series. He wears a white headband that conceals his Jagan Eye, which is placed on his forehead and has a purple iris. Despite his short size, he has a lean, muscular build to him.
His height is never mentioned in the anime or manga, aside from the DT reference. At the end of the series, an artbook puts him at 5' 3'. Hiei is the shortest of the four main characters at only 4' 10' during the Dark Tournament (excluding his hair) as stated by Juri.