白纸黑字 black and white
Explanation
比喻有确凿的文字凭据，不容抵赖或悔改。
It means there is irrefutable written evidence that cannot be denied or revoked.
Origin Story
从前，有个村子里来了个算命先生，他自称能掐会算，无所不知。村长不信，就拿出一个写满字的白纸，问他上面写了什么。算命先生故作神秘地念叨了一阵，结果完全猜错。村长指着白纸黑字说：『这上面白纸黑字写得清清楚楚，你连这都看不出来，还敢说自己会算命？』算命先生羞愧地低下了头，灰溜溜地离开了村子。从此以后，村民们再也不相信那些江湖术士了。
Once upon a time, a fortune teller came to a village, claiming to know everything. The village head did not believe him, so he showed him a piece of paper with writing on it and asked him what it said. The fortune teller pretended to be mysterious, but he guessed wrong. The village head pointed at the black and white words and said, "It is written in black and white here, and you can't even read this. How dare you claim to be a fortune teller?" The fortune teller was ashamed and left the village in disgrace. From then on, the villagers never believed in fortune tellers again.
Usage
主要用于书面语，多用于法律文书、合同等。也可用作比喻说法，形容证据确凿。
Mainly used in written language, often in legal documents and contracts. Can also be used metaphorically to describe irrefutable evidence.
Examples
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合同白纸黑字写得清清楚楚，不容抵赖。
hetongbaizhiheizixiedqingqingchuchu,burongdilaide.
The contract is written in black and white, leaving no room for denial.
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这笔交易，我们有白纸黑字的协议为证
zhebijiaoyi,womenyoubaizhiheizhidexieyiweizheng
We have a written agreement as proof of this transaction.