I recently had to re-install by Windows 7 OS to correct some corruption in the registry.  As part of that re install,I had to re-install Windows 365 as well.
(I've been a subscription user of Office 365 since March 2013).  When I re-established my outlook calendar (I forgot to save my outlook files before replacing the  OS) I noticed two things.  No more could I use categories for my calendar entries and the use of more than one color on the calendar was not possible.  I tried to add the categories function to the tool bar, but it limited itself to "New Tab".  I don't  even know how to access this "new tab"

I simply don't see how it is possible for the formatting of the basic program to change  upon re-install of the central software.