Killua has spiky silver hair, very pale skin and blue eyes. His eyes change shape depending on the mood that he's in, narrowing and sharpening when he goes into assassin mode. Killua is fairly lean at the start of the series, due to constant physical conditioning and torture training he received when he was young. As time passes, he becomes more muscular and toned. In the Nippon Animation anime adaptation, Killua's eye color is changed to green during the OVAs. He is also often seen holding a green skateboard (turned yellow in the 2011 series). Killua typically wears baggy clothing, with his usual attire consisting of long-sleeved and dark-colored shirts.
The most common cause of cauliflower ear is a hit to the ear -- or repeated hits to the ear -- that leads to hematomas, or small collections of blood that clot and block the flow of blood and nutrients.
Indeed, this particular cause of otalgia is due to Cranial Nerve 5 that transmits pain involving the jaw to the ear itself. Sometimes the pain/discomfort is due to a non-biologic trigger, like cell phone use (read more about this here). There are many other examples of non-ear causes of otalgia.