Reflector decoded baml as (an excerpt)
<GeometryDrawing.Brush>
<LinearGradientBrush LinearGradientBrush.StartPoint="0.522284,1.81298" LinearGradientBrush.EndPoint="0.522284,-0.812977">
<GradientBrush.GradientStops>
<GradientStop GradientStop.Color="{DynamicResource {x:Static SystemParameters.AppWorkspaceColorKey}}" GradientStop.Offset="0" />
<GradientStop GradientStop.Color="{DynamicResource {x:Static SystemColors.ControlLightLightColorKey}}" GradientStop.Offset="0.538136" />
</GradientBrush.GradientStops>
</LinearGradientBrush>
</GeometryDrawing.Brush>
but this is wrong - SystemParameters.AppWorkspaceColorKey
it shall be SystemColors.AppWorkspaceColorKey
<GeometryDrawing.Brush>
<LinearGradientBrush LinearGradientBrush.StartPoint="0.522284,1.81298" LinearGradientBrush.EndPoint="0.522284,-0.812977">
<GradientBrush.GradientStops>
<GradientStop GradientStop.Color="{DynamicResource {x:Static SystemParameters.AppWorkspaceColorKey}}" GradientStop.Offset="0" />
<GradientStop GradientStop.Color="{DynamicResource {x:Static SystemColors.ControlLightLightColorKey}}" GradientStop.Offset="0.538136" />
</GradientBrush.GradientStops>
</LinearGradientBrush>
</GeometryDrawing.Brush>
but this is wrong - SystemParameters.AppWorkspaceColorKey
it shall be SystemColors.AppWorkspaceColorKey