I tried to replicate the problem in telerik version 2012, 2, 607, 40 and it worked as expected at my end. Following is the sample code that I tried and attached is the screenshot.
sender, SchedulerEventArgs e)
e.Appointment.BorderColor = System.Drawing.Color.Red;
e.Appointment.BorderStyle = BorderStyle.Solid;
e.Appointment.BorderWidth = Unit.Pixel(10);
Please elaborate your scenario if it doesn't helps.