If the RowHeadersBorderStyle property is set to anything other than Single, the GridColor property must be a system color.
You cannot set this property to the Custom value, which is a read-only value indicating that the border style has been customized through the use of the AdvancedRowHeadersBorderStyle property.
If visual styles are enabled for the application through the Application.EnableVisualStyles method and the EnableHeadersVisualStyles property is true, the row headers are painted using the current theme. In this case, the value of the RowHeadersBorderStyle property is ignored for all row headers except the TopLeftHeaderCell, to which the theme is not applied.
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)