《淮南子·主术训》
当问盲乐师： 洁白的颜色是怎样的？ 他会说： 就像洁白的丝绸那样。 又问： 黑色是怎样的？ 
今日何为而义，旦日何为而荣，此难知也。问瞽师曰： 白素何如？ 
When asked of a blind musician: What is the color of white? He would say: It is like white silk. And what is black like? 