Color adds visibility to your Outlook items. Color categories can be assigned to
email messages in Microsoft Outlook, which enables you to quickly identify them
and associate them with related items. You can assign more than one color category to messages, or use a Quick Click category (Quick Click category: A default color category that is assigned to an item when you click the Categories column for the item in your Inbox or other table view. You set this color category from the Categorize menu.) to click once and assign a color category to a message
in your Inbox.
 
This is a a useful way to see, at a glance, e-mail from important senders, and it's a way to delay being forced to read spam e-mail.  If you receive a lot of e-mail, you probably can't color-code every single sender. But you can use this tip to color-code certain types of messages, such as those from your manager or your employees or even those sent just to you. more