By default, the OverviewColor property is -1, which indicates that the control's OverviewColor property specifies the overview-color to show the elements on the control's border. Use the OverviewColor property to specify a different color to be shown for specific elements. The OverviewColor property has effect when the element is not fitting the surface's client area and it is shown on the border of the surface. If the control's OverviewColor property is -1, no elements is shown on the border. 

The following screen shot shows the how elements are shown when they are not visible in the surface's client area ( look on the border ) :

The following screen shot shows the elements when they are visible on the surface's client area: