In the black is what every company wants to be: it means making way more money than the amount spent or owed.
The expression in the black means "making a profit" when used of businesses. When used of people, it means you're out of debt and only spending money you have. If you're in debt or losing money, you're in the red. Both phrases come from accounting, where black ink is traditionally used for positive values (like money you made), and red ink is used for negative values (like money you spent).