The following should be enough to remove the appointments background color and borders.
sender, SchedulerEventArgs e)
e.Appointment.BackColor = System.Drawing.Color.Transparent;
The above code will automatically set AppointmentStyleMode="Simple" for RadScheduler which will remove the appointment's borders.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed