Running Kubuntu 6.06. My HP Deskjet 3745 worked well for months, then took to changing from black to green in mid document. Now it prints in green all the time unless I specify another text colour such as red. If I specify some text as black instead of automatic it still prints in green. The red text is still red.
I have tried printing .pdf, .odt, and .txt, all do the same thing. However, when printing a ticket booking confirmation from the Internet, it appeared to be correct. Opening an HTML file and printing it comes out just as green as the rest.
This is the second HP Deskjet to play this trick on me, on different computers but the same OS. The first one went a nice shade of aquamarine. I tried changing the black cartridge but to no avail.

My inkjet printer started doing the same thing last week. The printer had been using the color cartridges to print black and they were running dry. I got into the CUPS web administrator and changed the setting from color printing to using just the black ink cartridge. That works for me because I don't print color documents/pictures.

You can start the CUPS web administrator interface by firing up a web browser and pointing it to localhost:631. If it asks you for a user name and password you can use the root account if your distribution allows it. Otherwise you will have to create a user account for administering CUPS. Instructions for that are in other posts on this topic.

As you suggest, CUPS requires a root login, which Kubuntu does not have. I am planning a switch to Debian Etch in the near future, I'll hold off until then rather than create a root user. Useful hint, thanks.

Finally got round to installing Etch, got into CUPS, set it to black, prints (everything) in black, which suits me fine.