介绍:
First one “in the red”
Originally it was used by the accountants in business or the stock market.
起初，这个词组的与商业中的会计有关。
The numbers in the financial records of a company were written in red ink to show a loss.
会计在公司的账本上记账的时候，用红色的数字代替亏损。
If someone is doing business at a profit, instead of using red ink, accountants will use black to write down the inficit.
如果有盈利，会计就会用黑色的笔标出赤字，而不是用红色的。
For example:
Eg: Since he is not good at doing business, his company will end up financially in the red.
由于他不擅长做生意，公司将在财政上以赤字告终.
Second one"red letter days"
A red letter day is any day of special significance.
This expression did not originate from Medieval church calendars or a requirement that important holy days be marked in red Instead, important days indicated in red in a calendar dating from the Roman Republic (509 BC-27 BC).
这个短语并不是从大家现在所知道的罗马教会在日历上用红色墨水在教会日历上为重要的节日做标识
Originally, the initial capitals and highlighted word were written in red ink. The practice was continued after the invention of the printing press, including in Catholic books. Many calendars still indicate special dates and holidays in red instead of black.
最初人们喜欢用红色标注大写的或者非常重要的字，而这个做法呢一直延生到纸的发明，到天主教派书慢慢有了，很多日历中现在还仍然在用红色标记特殊节日和重大喜庆的饿日子。
For example:
The day that I was born is a red-letter day for me.
我的生日是我每年重要的日子。
