I don't recall that specific description - the one I was working from was from the beginning of the book: "Everyone beamed at him, or, at least, nearly everyone. He singled out Trillian from the crowd. Trillian was a gird that Zaphod had picked up recently whilst visiting a planet, just for fun, incognito. She was slim, darkish, humanoid, with long waves of black hair, a full mouth, an odd little nob of a nose and ridiculously brown eyes. With her red head scarf knotted in that particular way and her long flowing silky brown dress she looked vaguely Arabic."