Allow categories for IMAP email messages; this can be with local folder category settings or using the categories of a connected Exchange/MAPI folder if it is selected as the default folder.
I'm trying to switch to Inbox Zero, but since a unified Inbox is not really possible because I do not get Send As delivery of connected accounts in Outlook.com, I can at least use color categories in my IMAP accounts.
Travis Day commented
When using Outlook to access IMAP email accounts such as Gmail, can Outlook Categories map/sync to Gmail Labels? That way, categories applied to email messages can be sync'ed to the (Gmail) server and would be viewed the same when accessed from different PC's.