What does the red mean?

[v0031]

 Tackle your debt
Roughly 40% of millenials have credit card debt, and the same percentage is paying back money they borrowed to pay for college or buy a car, You shouldn’t beat yourself up over being in the red, but you do need a plan for eliminating those liabilities, since excessive credit card debt and burdensome student loans can hold you back from reaching your financial goals.
If you owe money, create a debt repayment strategy. Getting a side job and negotiating the interest rate can allspeed up the process of paying off your credit cards. You could even try one of these five crazy ways to pay off your student loan.

[True Federalist (진정한 연방 주의자)]

Two separate idioms are in the red.

"Beating yourself up over something" means being excessively critical of yourself.

"Being in the red" here refers to being in debt.  It refers to the accounting convention of using red ink to mark negative amounts in the ledger of accounts. (An equivalent convention is to enclose negative amounts in parentheses if only one color of ink is being used.)

The odd thing is that properly done, almost no negative entries occur in double entry bookkeeping. Most accounts are intended to consist solely credits or debits, and their entries are entered as positive numbers in black ink, with red entries usually indicating the correction of an error or a reconciliation with another account.  The most common account in which there is no default direction is the account which tracks profit or loss, in which case by convention black ink is used to indicate a recorded profit and red ink (or a pair of parentheses) is used to indicate a recorded loss.

However, while losses are marked in red ink, debts are usually marked in black ink as they are recorded in a liability account where repayment of principal would be marked in red ink. Hence, strictly speaking "being in red" shouldn't be used to refer to being in debt, but most people don't know or care about the minutiae of accounting but they do know that red ink often indicates undesirable results.