I've only had this happen once and it also cut off the print. I think it was also grey. I'd be interested in others experience.
Same experience with me -- but it happened when I ran out of gloss enhancer
My conclusion is that the HP Z3100 is not as well designed as the Epson 4000 in this regard. (HP, are you listening? Can you correct this in firmware? I assume so, and can only hope that you'll do so.)
For the benefit of HP, with the very old Epson 4000, when it runs out of ink it just stops printing and waits patiently for a new ink cartridge. When the new cartridge is installed, printing resumes and it is seamless. On BOTH the 4000 and the HPZ3100 it is important to print to the very end of a cartridge because the ink indicators aren't accurate and will lead you to believe that a cartridge is empty when it is not. By printing all the way to the very end, you get a significant number of additional prints.
So, with the 4000, you keep printing until the cartridge runs out of ink, and then you replace it.
No wasted paper, no wasted prints, no wasted ink.
HOWEVER, when a new, supposedly state-of-the-art Z3100 runs out of ink, it does all three
* it wastes the print
* it wastes the ink from the print
* it wastes the paper from the print
And, last but not least, it wastes our time.
So, HP will you fix this in the next firmware release?