Killua spots a spiky, silver hair and blue eyes (green in the anime/OVA version), which change depending on the mood that he's in. Narrowing and sharpening his eyes signifies himself getting into assassin mode.
Killua typically wears light turtleneck blue baggy clothing, with his usual attire consisting of long-sleeved and dark-colored shirts. Killua also wears long, baggy shorts in the manga and Madhouse animated adaptation, but Nippon Animation's character design gave him a different treatment by shortened them to reach above his knees. Killua also wears blue boots, recolored brown and black in the Nippon Animation adaptation.
The HUNTER×HUNTER Quartet（Gon Kurapika Leorio）
Zoldyk（Illumi Milluki Killua Alluka Kalluto Zeno Silva）
Chimera Ant Hunters