Outlook uses color for contact categories, but it is always good to have a name for the category, which is much easier to remember. Please see below for details:
Step 1: Click "People" button to open the contact window;
Step 2: Click the "Categorize" button in the "Home" tab;
Step 3: Choose "All Categories" from the drop-down list;
Step 4: In the "Color Categories" window, choose the category you want to rename and click "Rename";
Step 5: Type a new name for the category and click "OK" to complete.
