Spelling mistakes are circled in red ink.

拼写错误都用红笔圈了出来。

《牛津词典》

The U.S. Postal Service (USPS) continues to bleed red ink.

美国邮政管理局继续亏损。

youdao

Citi almost drowned in the red ink.

花旗几乎被赤字淹没。

youdao

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

The challenge was daunting: The electronics and entertainment giant was struggling with red ink and management paralysis.

FORBES: It Takes a Crisis

Red ink disappears by 2019 if spending is allowed to grow 1 percent each years.

FORBES: New CBO Numbers Confirm Modest Spending Restraint Can Balance The Budget

Painful revamping of a poorly integrated expansion led to red ink in 2001 and 2002.

FORBES: Ready, Aim, Fire