Currently, color coding of event copies relies on the default Outlook category names. (“Blue category,” “Green category”, etc.). For users who have renamed their Outlook categories, the instructions describes the current work around (which will be rendered unnecessary in a future release).
In Outlook you can see the names of your categories from the Home Tab:
If you have previously renamed the category of the color you want to use for your event copies. You can either rename the category back to its default name, or you can create a new category. Just click the “All categories” button in the menu shown above, and then either rename the existing category or add a new category. In the example shown below, the Blue category had been renamed to “Renamed category” so the user has created a new “Blue category.”