The ink has run out.
Replace the cartridge.
However, you can print in black-and-white as long as there is K (black) ink in the print cartridge.
To resume printing, press the [FormFeed], and then the [OK] key.
If you continue this type of printing, the amount of ink consumed for the next print cartridge replacement will be greater than usual.
See Replacing a Print Cartridge.
If the cartridge is empty, head cleaning or flushing cannot be performed.
If the ink runs out during printing, the machine may eject blank or partially printed sheets.