Assigning messages to categories can help you more easily locate information. Outlook 2007 introduces the Color Categories feature, which combines named categories with color bars to provide an immediate visual cue when viewing messages in your Inbox.
You can apply color categories to messages, calendar items, contacts, tasks, and notes. You can apply color categories several ways:
In any folder, you can select one or more items, click the Categorize button on the Standard toolbar, and then click the category you want.
The Categorize button might not appear on the toolbar until ...