property Thumbnail.KeepOriginalThumbnail as Boolean
Specifies whether the thumbnail is shown as it is provided.

TypeDescription
Boolean A boolean expression that specifies whether the thumbnail is displayed as it is provided, in other words without using a transparent backcolor. 
By default, the KeepOriginalThumbnail property is False. Use the KeepOriginalThumbnail property to retrieve bitmap thumbnails using transparent background color ( implementation removes the black part of the thumbnail view ). Use the BackColor property to change the control's background color. Use the Borders property to specify the size of the margins where the thumbnail picture is displayed. Use the Picture property to display a picture on the control's background. Use the PictureDisplay property to layout the control's Picture on the background.