In the past, numbers in the financial records of a company were written in red ink to show a loss.

VOA: special.2009.04.26

but I mark the whole paper up with a lot of red ink if there are mistakes,

但我在批论文的时候，也会把语法错误的地方用红笔标出来，

与哲学系教授 - SpeakingMax英语口语达人