[Locke.]

Also, on his eye:

Euron is pale and handsome with black hair and a dark beard. He wears a patch over his left eye, and is nicknamed '"Crow's Eye".

According to Euron's nephew, Theon, the patch conceals a "black eye shining with malice"

So he actually does have both eyes, and Theon hasn't known him since he was a child so his view on it being "black" could just be a story he'd been told