1、not worth a red cent
e.g. I don't know how I'm going to tell that woman that her prized collectibles are not worth a red cent.我不知道我要怎么告诉那位女士，她珍贵的收藏品其实一文不值。
a red cent
a cent is the smallest coin in value in American money and is worth very little.
2、a red eye
an overnight airplane flight. a flight that leaves late at night and arrives early the next morning
e.g. We took the red eye from Seattle to NewYork.
3、a red-letter day
a day that is very important or very special
e.g. The day our daughter was born was a real red-letter day for us.我们女儿出生的那一天对我们来说真的是非常特别的一天。
4、(boy,) is my face red!
An exclamation of acute embarrassment or mortification.
e.g. I can't believe I was calling my client by the wrong name. Boy, is my face red!
e.g. I spent so long on that report, only for it to be laughed at by everyone in class. Is my face red!我在那篇报告上花了那么长的时间，也只是被班上每个人嘲笑。真是太丢脸了！
5、red as a cherry
同样用法的还有：red as a poppy; red as a rose; red as a ruby; red as blood
e.g. When she came in from ice-skating, Clara's nose was as red as a cherry. 当Clara滑完冰回来，她的鼻子红彤彤的（像樱桃一样红）。
e.g. When her boss praised her in front of the whole office, Emily turned red as a poppy. 当Emily的老板在整个办公室前赞赏她，她脸一下子就红了。
official rules which do not seem necessary and make things happen very slowly
e.g. My passport application has been held up by red tape.
e.g. Because of red tape, Frank took weeks to get a visa.
e.g. Red tape prevented Jack's wife from joining him abroad.
to be very angry.
e.g. Bill really saw red when the tax bill arrived.
e.g. Some Internet customers are seeing red as a result of the new virus that slowed Web traffic last week.上周一种新的病毒减拖慢了网络流量，一些网络用户对这个结果十分生气。
e.g. When he laughed in my face, I just saw red.
8、red sky at night, shepherd’s delight
A red sky at sunset is a sign that good weather will follow. The full phrase is "Red sky at night, shepherd's delight; red sky in the morning, shepherd's warning.”
e.g. I think we're going to have a nice sunny day tomorrow. Look at that sunset—red sky at night, shepherd's delight.我想明天将会是一个美好的晴天。你看那个日落——晚霞晴。
debt; indebtedness as shown in red ink on a financial statement.
e.g. There is too much red ink in my financial statement.
e.g. Too much red ink and the company will collapse.
和它相对的是：out of the red
out of debt; into profitability.
e.g. This year our company is likely to get out of the red before fall.
e.g. If we can cutdown on expenses, we can get out of the red fairly soon.
10、paint the town red
to go out and enjoy yourself in the evening, often drinking a lot of alcohol and dancing
e.g. Jack finished his exams today so he's gone out to paint the town red.
e.g. They were out painting the town red last night.