Devexpress DiagramControl以编程方式创建Shapes

如何解决Devexpress DiagramControl以编程方式创建Shapes

嘿，我想创建一个图表，但是当我开始我的项目时，形状没有任何颜色，WPF窗口中只有文本

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            DiagramContainer diagram = new DiagramContainer();
            DiagramShape startShape = new DiagramShape();
            startShape.Shape = BasicFlowchartShapes.Decision;
            startShape.Content = "Start";

            diagram.Items.Add(startShape);


            DiagramShape Shape2 = new DiagramShape();
            Shape2.Shape = BasicFlowchartShapes.Decision;
            Shape2.Content = "Middle";

            diagram.Items.Add(Shape2);

            DiagramGrid.Children.Add(diagram);
        }
    }