Why can I no longer use my own color categories in Outlook calendar?

[paulkaye]

I work in a team, and we use a shared Outlook calendar. I used to be able to create and use my own color categories for calendar items (e.g., so that I could quickly identify them as mine). Now the option to create a new color category is grayed out. I believe this started when we moved from our own Exchange server to Office365. Could that be the cause of the problem? Is there any way to get this functionality back?