Losing money. Being in debt.
亏损，欠债；
it's believed this phrase originates from accountants who are selective on which color ink they use when making entries in a firm's book.
传说这个词组的来源与会计有关。会计在公司的账本上记账的时候，用什么颜色的笔很有讲究。
If someone is doing business at a loss, instead of using black ink, accountants will use red to write down the deficit.
如果有亏损，会计就会用红色的笔标出赤字，而不是用黑色的。
Indeed, the color red is prominently used in businesses to signify a loss, while black is used to indicate a profit.
的确，在商业环境中，红色常常用来表示亏损，黑色用来表示收益。
Thus, a company that's interested in making money would desire to be 'in the black' rather than be 'in the red.'
因此，想赚钱的公司都很希望自己是in the black而不是in the red.
This idiom seemingly originates from the early 1900s.
这个词组应该是起源于19世纪。
There are numerous newspapers from that period of time which use the phrase when referring to businesses functioning at a loss.
在那个时候，有很多报纸，上面用到这个词组来描述亏损的企业。
For example, the Daily Globe from 1927, under the subheading 'Failed to get Interest,' reads:
比如，Daily Globe在1972年的副标题为Failed to get Interest的文章中这么写道：
"I regret to report to you that the people who put money into it failed by $30,000 to earn even operating expense and depreciation. The company is in the red all the time."
我很遗憾地告诉大家，投钱进去的人亏损了3万美元，甚至连营运和折旧费用都没有赚回来，公司一直在亏损之中。
For example:
举例：
1.His company, however, ended up in the red. It lost more money than it earned. The company was no longer profitable.
但是，他的公司最后还是亏损了。亏的钱比赚的还多。现在已经不盈利了；
2.Work out how much sleep you owe your body and find out how to recover if your sleep account is in the red.
算出你到底缺少了多少睡眠。如果你的睡眠帐户处于赤字的话，要用多少时间来补。