Try setting CSS class for appointment in AppointmentDataBound event and see whether it is working fine. Checkout the following link for more information: Setting styles for appointments
I have some limitation to specify the a css class.
becase the colour is determined by some condition in my apllication.
the colour may varry from #000000 to #FFFFFF
so i cant make that much of css calsses :(
so i should have to go for some dynamic way