The BackgroundPartEnum type indicates parts in
  the control. Use the 
Background property to
  specify a background color or a visual appearance for specific parts in the
  control. A Color expression that indicates the background color for a
  specified part. The last 7 bits in the high significant byte of the color to
  indicates the identifier of the skin being used. Use the 
Add
  method to add new skins to the control. If you need to remove the skin
  appearance from a part of the control you need to reset the last 7 bits in the
  high significant byte of the color being applied to the background's part.