Changing the "Category" property on an Outlook.Appointment Item

I have written a VSTO Outlook addin in VS2008. I can catch the
Outlook.Appointment item within the ThisAddin.Item_Add event. I set
the category of each item to an Outlook define category type. The
category is saved correctly to the Outlook.Appointment item, however,
at this point the Outlook.Appointment item has already been displayed
within the Outlook Calendar, which mean the color of the category does
not get displayed.

When I got to the Inbox and back to the calendar of interest the
Outlook.Appointment item still does not change color to the category
that I set within the Addin. When I close Outlook and then reopen
Outlook the Outlook.Appointment item category color is displayed
correctly.

Is there a way that I can set the category and then have Outlook
reload the item so the color of the category can be displayed within
the same session?

Thank you for your time.

-Morna