Printing in grayscale in POP!_OS

I’m trying to print some documents in grayscale / black & white but it keeps printing my documents in colour instead, even if I select grayscale in one of the drop down menus in the settings (under Color > Color Model).

Does anyone know if there is a specific setting I need to change for it to print in grayscale correctly? If it helps, I have a Canon MX420 printer.

Thanks so much for your help!