Hi, welcome to the Apple Users Community.
When the printer was setup on your Mac Mini a PPD/driver installation occurred. Can you please compare this with another device on your network and confirm they are the same driver? If not then please try step one below.
- If you visit the HP website on your Mac Mini, the site will detect the OS you are using and help guide you to the correct driver to install. The Apps you use are not going to help change whether you print on color or BW until the correct driver is installed.
- If the driver is correct then you will need to check the settings within it without any apps open. Go to "System Preferences" and look for the "Printers and Scanners" icon, clicking it will bring up a list of connected devices you have setup. The HP printer will be there if it has been installed correctly. If a "Generic Device" printer setup is showing that is a likely cause of the BW printing.
If you cannot affect a change using these steps reach out again and I'll be happy to assist.
Best of luck