Usopp was clearly frozen, with surprise or anger Kamui didn't know. It was hard to read the guy's face through that slapstick banana peel. Seriously, what a waste of good fruit... Still, Kamui wouldn't find out whether Usopp was mad or not unless he provoked the poor guy out of his shock. Being proactive was always best.

Kamui relaxed his shoulders and grinned. "Yellow is definitely your color."