The use of the three color ink cartridges may vary. However, you are able to see the level of each ink cartridge. There is a symbol for ink shown in a small window on the printer. Clicking the ink drop symbol next shows levels for each color cartridge, including black. You only replace the one that needs it. By the way, you may get a message a particular ink cartridge is low; keep using it! Usually you can do a lot more printing before the ink actually runs out!