Assuming this is on Windows 10 Anniversary (Version 1607), then see here for the MS fix.
If not only Win 10 1607, then make sure you are not modifying Printing Preferences (Applies to local install)
in place of Printing Defaults (Pushes to clients)
Hi there. Our organization just received a 7855 workcentre and we've been trying to set the default on the print server (2012R2 with PCL6 drivers) to black and white. The problem we are running into is while the setting "Xerox black and white conversion" stays the same on the print server, when a user adds the printer his defaults are still not going to black and white. Any help on this would be appreciated.