From the obscure bug (or is it a feature?) department:
When you turn the reading pane off or set it to the Bottom, you’ll see all of the field names, with Categories on the far right. If you move the Category field to the left of the From field, you’ll see only the category names – the category color swatch isn't displayed. This bug was introduced in Outlook 2010 but I only recently started seeing complaints about it, as users upgraded to Outlook 2013.
You can easily trick Outlook into showing the color swatch by changing the format of either the either Importance or Reminder field to display text. (You only need to change one field to text format.)
To make this change, right-click on the row of field names and choose View Settings, then Format Columns. Change Importance to use Text with popup list format or Reminder to use Yes/No format and the color magically returns.
Published November 21, 2014. Last reviewed on November 21, 2014.