With the exception of the All Fields page of an Outlook contact, the only way to add categories to items is using the Category picker menu or dialog.You can use the All fields page to bulk add categories to Outlook 2007 or Outlook 2010.
As of Outlook 2007, Outlook does not use the registry for a master category list; they are stored in the default message store (mailbox or pst).
If you are setting up a new system and using your old pst the color categories will be available on the new system.
(nn = your version of Office.) To print a list of the category names and their colors, we have a macro and instructions Print a list of Categories and their Colors.
How to Upgrade to Color Categories in Outlook 2007/2010 (video tutorial) Unlike with older versions, you cannot paste a comma separated list of categories into the master category dialog and add them all to the Outlook 2007/2010 master list.
Outlook has always supported categories, in Outlook 97 through Outlook 2003, they were simply Categories.
Outlook 2007 introduced Color Categories by merging the short-lived colored flags with categories.