Background color settings of the internal portion of the button surface when a special effect has been applied (see SpecialEffect property for details about special effects).
If this color should be left undefined, the ColorSurfaceNormal property settings would be kept: you can swap the colors of the internal portion with the colors of the external portion through the SwapEffectsColors property.
This property is ignored when the Surface property is set to Surfaces.VistaAero, Surfaces.Office2003, Surfaces.Office2007 and no special effect has been set through the SpecialEffect property.
This property encapsulates the functionality of the SurfaceColor class.
In order to perform changes to color settings at Design-time take a look to the How to change the control colors section.