Thanks, but no joy.
I tried downloading the Hp diagnostic tool and it turned up nothing new. The page the diagnostic printed looks "reasonably close" to the image of what the page should look like. However, it still exhibits problems. The blue color box has a very faint horizontal line which is a lighter blue. The black color box has a very difficult to see black line about 2/3 of the way down which is exactly at the same position as the very faint line in the blue box. The magenta and yellow boxes are good. The image has a line which changes color as it crosses the image, at exactly the same position as the line in the blue and black boxes. The line is grey where it goes through the tipped over vase, and a darker grey where it passes over the picture in the frame and the white pitcher standing upright and the urn behind it. It is also black where it passes over the blue cloth. The text and black boxes of bands and hatches look fine.
I am pretty sure it is a problem with the printer itself, as the problem exists regardless of the program which prints the image, and it exists when printed from both a unix system and a windows system. The printer is on the network, not connected directly to a machine, and the firmware is the most recent (DLM1FN1006BR).