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.
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.
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!
我不敢相信我竟然叫错了客户的名字。真是太难堪了!The China Red中国红