EDIT: Sorrily, I see after more testing that while the below settings (adding CNGrayscale) can do the job, the solution is not too convenient because the change is not remembered... It can still be used as a last resort...
I have tested this in Xfce, not in KDE. Initially posted here.
In System - Printers, selecting the printer's properties, going to "Job options" - "Other options", down at the end there is an empty field to add a new option; fill that field with CNGrayscale and click "Add".
The new option is now listed under "Other options", but has an empty field: fill that with TRUE, then click "Apply".
Now the new option CNGrayscale has a true/false switch that you can use to change between color and monochrome printing.
This seems to be related to availability or correct selection of drivers. Printers connect in different ways, and drivers can be selected automatically or manually. A solution might be to try adding the printer manually in a way that gives choice between different drivers that can be in this way tested.
For example, in my case, I was able to add the proper driver by connecting my wifi HP Officejet 3833 printer by USB cable to my internet modem/wifi box then, following this method that is specific to my internet provider I have added new printer, selected Network printer > AppSocket/HP JetDirect, then entered my provider-specific data under Location of the network printer - Host:, then, selecting a driver from the database, I have selected HP; all Officejet numbers 3830 to 3834 had the same 3 drivers available:
The first in the list, which is marked 'recommended' was the one selected the last time and which entailed the very problem I was trying to solve. So, I have now selected the second one, the one that says 'hpcups' (the printer being HP).
The third is
hpijs; these two drivers come from HP and are based on
hplip, as said here, but when testing both I see differences in the printer properties' interfaces: the
hpijs driver doesn't have a color settings under "Printer options", and changes of the one under "Jop Options - Other options (Advanced)" are not remembered. So,
hpcups is the good one for me.
In this way I have added the printer which, under Properties > Printer options > Color mode, now shows, beside Color, another two Grayscale options (High quality and Black only).
So, this seems a driver issue.
3.17 version worked for me, but there is also a newer version of the driver that can be installed like in the askubuntu answer here, redirecting to the HP page here.