雌黄 is an actual yellow mineral, arsenic trisulfide (As₂S₃). Ancient Chinese scribes used it as an early correction fluid: dabbed onto bamboo or yellow paper, it covered miswritten characters. From this came the famous idiom
信口雌黄 (xìnkǒu cíhuáng) — literally "orpiment from the mouth" — meaning "to spout corrections irresponsibly," hence "to talk nonsense / slander baselessly."
