1. Open Outlook 2010 for Windows and log into your Exchange account.
2. Click on the Calendar button in the lower left corner of the Outlook window.
3. Right-click the existing meeting you wish to assign a category. Go to Categorize and select the category and color you wish to use.
4. If it is the first time using this category, Outlook will ask you to set up the category. You can change the category names and colors at any time. Click Yes. The meeting is now assigned to that category and color.