You'll need to change this setting for each calendar style you use.
If you delete the OutlPrnt file to fix printing problems, the calendar will be set to print in gray scale again. If you can print to PDF in color by the printer prints in gray scale, the problem is with the printer. Even with this set to gray shading, some colors will print, including the background colors for events spanning more than one day and events marked busy will have a purple icon on the Agenda style.
