I found a solution to this! It's a little bit of a workaround but it works so solidly that I have to recommend it. Just follow the steps and your HP OfficeJet 6500 will be able to use only it's black cartridge without any hassle on your Mac.
1. Start a virtual machine and VMware fusion, virtual box or Parallels and begin a virtual machine with Linux Mint. (Note: I know it's a bit much for one step but it's totally worth not having to pay for another printer or only using color ink for every black page that is printed.)
2. Connect the virtual machine to your network.
3. Open "Software Manager" in the start menu and install "hplib-gui"
4. Open "hplib toolbox" in the start menu and search for your printer here whatever connection you're using for your virtual machine (you don't need to search term to find it).
5. Once you're connected to your printers you will be provided with extensive controls that we would prefer to have on the mac that will be able to completely control everything that you need for your printed document including more layouts than the Mac had.
6. Now go to the "General" tab and then "Output Mode" select the option "black only grayscale".
7. Unlike the Mac's grayscale mode this one actually will force the printer to use only the black cartridge for the printing operation.
8. Hit "Print File".
9. Now get back to work and wasting your time fussing over a printer that should've been built like this for all operating systems.
🙂 Have a nice day.