Interesting! Similarly, in English we would say that a business was "in the red" if its expenditures exceeded its income. (Or something like that. It's a colloquialism, so it doesn't really have a specific technical meaning.)
This is because losses were traditionally written in red ink back when books were done on paper. Profits were in black ink which is why profitable businesses are sometimes referred to as "in the black."
Typewriter ribbons that were 2 colours were always black and red. (I presume that was a carry over from when your main ink would have been black or possibly blue, and the alternative would have been red).
As your normal credit entries would have been black, if the "bottom line", the sum of your accounting book column was negative, showing a loss, you would emphasize it with the red type.
