Xanthus was the immortal horse of Achilles, just as Balius was. He was the son of Zephyrus (the west wind) and the Harpy Podarge. As a colour, xanthus basically means 'yellow', but for a horse's coat, as here, it can also mean 'bay', 'chestnut' or 'golden'. Perhaps, though, the colour refers more specifically to the horse's mane, in which case he could even be a 'palomino'.