Print color as gray option not working

[Sergio Callegari]

Seen on an HP Color LaserJet Pro MFP M281fdw using arch/manjaro linux.

This issue makes it impossible to print in grayscale and is serious as it hits quite heavily on printing costs making the printer economically unsustainable.

Now, the weird issue is that using ubuntu, the printer seems to respect the Print color as Gray option. However:

(i) Ubuntu has a much more dated version of hplip, so this may be a regression; or

(ii) Ubuntu seems to build differently the PPD files. In arch/manjaro, the relevant PPD file
includes the strings:

*HPPJLColorAsGray True/On: "%%"
*HPPJLColorAsGray False/Off: "%%"

While in ubuntu there are the actual commands to switch on/off the grayscale printing. Questioned about the matter, arch responded that they do not touch the upstream package while ubuntu likely patches it to have the PPDs generated dynamically.

[Sergio Callegari (callegar)]

If you manually add "@PJL SET GRAYSCALE=COMPOSITE<0A>" in place of "%%" in the *HPPJLColorAsGray True/On: "%%" then printing in gray works.