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My question:
Dear teachers
please tell me what is the differenece between "in
the red" and "in the black"? and what is their usage, because I am confused by these two phrases.

Answer posted by Robert
In the world of finance and accounting, 'loss figures' are traditionally expressed in 'red'; 'profit figures' are expressed in 'black' on the 'profit and loss' statement.
Thus, in any given time frame, a quarter, a fiscal year, for example, if you have incurred a loss, you are 'in the red'. If you have made a profit, you are 'in the black'.

My comment
At first, aftet I sign in and post my quesiton in the board, it takes about half an hour then my post has finally been posted, which annoys me for its inconvenience. But to my surprise, it takes only about an hour then somebody answers my quesiton so quickly or maybe my question is too easy for native speaker, I don't know.
Moreover, Robert' answer is preciely correct and in detail. He gives what I really want to know and even provides an example for me. This site is trully a website that can help we ESL learners, and I hope somedays I can raise other in-depth qustions and to have a discussion with those post respondents.