Color filters unread documents

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I have over 1000 documents to review and I am seeking a method to automatically identify unread documents using a color filter.

While I understand that important documents can be manually annotated after being read, I am hesitant to annotate all read documents as it may include unimportant ones.

Consequently, distinguishing between unread and unimportant but read documents has become challenging for me.

How can I automatically mark unread documents in order to differentiate them, similar to the way unread emails and posts are marked?

What steps should I take?