[Evolution] Category Icons in Calender

[Robb Westby <robbw mxim com>]

I am trying to add my own category icons in the Calender program. 

For example when you set an appointment (File > New > New Appointment)
you can select a Category to have the appointment included. Once you
save the appointment an icon (a flower in flower pot for the Personal
Category) appears in the viewing of the Calender. 

Is there documentation someone can point me towards to include my own?