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I think that your problem may be owing to software on your computer - at any rate, it is to-be-tried. I am aware that you consider yourself to have eliminated the driver. You say that you used the Color Copy option... did you use the Copy Color button on the HP machine itself, and try copying a page with both color and black in it? I advise doing that, and seeing if, that way, the black is not reproduced in the page.
Also, please tell me what cartridges you are using, esp. the current black ink cartridge? are they HP-OEM-original or are they 'HP Compatible' or refills, remanufactured, rechipped, etc.?
What is your computer, a Windows PC or an Apple computer?
Which version of Windows (or MAC OS X ) is on it?
(If a Windows PC, what is its System Type? either 32-bit or 64-bit, and found inStart - Control Panel - System and Security - System .)
Thanks for the detailed rundown; that is a confusing set of symptoms and problems.
Check the Ink Levels, first, I advise. In an attempt to simplify the problem, we need to see if the black ink is low.
I have an idea about a simple root to this problem: the black ink may be running out, unrecognized at times because the cartridge is flakey, or it might be a 'HP compatible' cartridge rather than an HP-OEM-original cartridge... HP's cartridges (the genuine ones) are very precisely made to be recognizable and to eliminate the use of non-HP or non-OEM cartridges, so whatever black ink cartridge you have in the printer may be intermittently not recognized, instead of being low or out of ink.
In HP printers, when the black ink runs out, the printer can switch to using the three color inks together to produce a 'black' from a mix of all three colors. This 'mix' mode can produce grayscale printing and 'black' text printing. It helps the printer get past a running-out or other disabling of the black ink, but it runs down the color inks much faster.
So in short, for all these reasons, I advise replacing the black ink cartridge. I explained this in detail, in order for you to see why I make a simple recommendation for a complex problem... it might possibly amount to just that needing to be done.
And when the black ink is replaced, of course, replace it with a genuine HP cartridge.