If you choose to completely customize the appearance of the C1Schedule you may not wish to use any of the available built-in Visual Styles. In that case, to override any visual styles with your own custom appearance, you will need to set the C1Schedule.UseEmbeddedVisualStyles property to False.
By default C1Schedule.UseEmbeddedVisualStyles property is True and Visual Styles are used. Any customizations you make while using Visual Styles will simply set specific elements in the control's appearance on top of the current Visual Style. To start customizing the control's appearance from scratch set C1Schedule.UseEmbeddedVisualStyles to False and set your own styles.