Why are the Unity voicemail messages in Outlook color coded?

When Unity voicemail is enabled for your account and is set to deliver voicemail messages into your email, a new Outlook category called “ViewMail” is created in your mailbox, which you will see in Outlook Web Access (OWA) via https://mail.kent.edu and Outlook (Mac and Windows) . 

All voicemail delivered into your mailbox will be assigned this category automatically. This feature allows new voicemail messages to be identified based on this category assignment, allowing you to easily search or sort your voicemail messages by that category or color. 

The color assigned to the ViewMail category will vary, not only by user, but also through the email client you are using. For example, if one user accesses email through OWA, Outlook for Mac, and two different computers with Outlook for Windows, each could have a different color assigned to this category because it is not a system-wide setting. That setting is made and retained by the client used for email access.. 

Not only will the colors for the category differ, but how the category colorization is observed in the mail client will also differ. As you can see below, Outlook for Mac will change the color of the entire message in your Inbox, based on the color set for the ViewMail category. OWA and Outlook for Windows, however, utilize small squares to the right of each message in order to identify the category of the message. 
Outlook for Mac 

OWA/Outlook for Windows