People who print calendars discovered that Outlook is no longer printing colors by default. This is caused by a change in the print options in the recent update.
The default Print Option is to use gray shading. This is not new – Print using gray shading has been the default since at least Outlook 2007. But in older versions and builds, gray shading applied to header areas, not category colors. The recent update changed this behavior and category colors are not printed in color when 'print using gray shading' is enabled.
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.
If you can print to PDF in color by the printer prints in gray scale, the problem is with the printer.
If you delete the OutlPrnt file to fix printing problems, the calendar will be set to print in gray scale again.
You'll need to change this setting for each calendar style you use.
Printing Black and white Calendar in Outlook for Mac
Like Outlook for Windows, Outlook for Mac defaults to printing calendars in black and white. If you want to print colors, in the print dialog, click Show Details (lower left of the dialog, where Hide Details is in the screenshot). You’ll have a number of customizations to choose from and the last one on the page is to print in black and white. Untick the option and print. Click Hide Details to revert to the smaller print dialog.