A ChartInterior object contains formatting properties of a ChartRegion or an object extending ChartRegion ( AxisLabel, ChartText, Legend, or SeriesDataLabel ).

 public sealed class ChartInterior

Public NotInheritable Class ChartInterior

property of the following classes: ChartRegion, AxisLabel, ChartText, Legend, and SeriesDataLabel.

If the pattern is Solid, you should set the fill through the Foreground color. The background color is the incorrect way to set a solid fill.