When a color cartridge runs out, I can't print in black either. I rarely even use color.

[s-m-]

On my OfficeJet color printer, even when one of the color cartridges run out, I can't print in black either. All I really need is black ink anymore. I don't use color, other than a word here and there on a document. I'm sure this is intentional on HP's part to sell more ink, but is there a workaround? I can't keep buying color cartridges just to print black.

[Bob_Headrick]

HP and other printer manufacturers have different printer technologies for different needs.  For inkjet printers:

• Some have printheads built into the ink cartridges.  These printers can typically print with one or more of the colors completely empty, or even with color or black (but not both) cartridges removed. The Officejet 8040a is an example.
• Other printers have separate ink supplies and replaceable printheads.  An example would be the Officejet Pro 7612.  The printhead in these printers can be replaced if they are damaged by running the printhead with colors out.  Some of these printers will allow printing with a color out, others will not.  If the printer is run without ink in one or more colors the printer may be damaged, but the user may be able to recover without having to send the printer for service.  (Replacing the printhead, while it can be done without sending the printer in for service, is expensive.)
• Other printers have permanent printheads.  To run these without some ink in all the colors would risk causing damage to the printhead due to clogs, air ingested in the printhead or burned out printhead firing resistors. The Officejet 6700 is an example of this type of printer. For printers with fixed printheads this could require service to get the printer to print properly again when the ink is finally replaced.  

The document here describes how ink is used.  While the document is written for HP Inkjet printers the same principles apply to inkjet printers from other manufacturers as well.