c# OxyPlot为曲线下的图形着色

using OxyPlot;
using OxyPlot.Series;

public PlotModel CreateAreaChart()
{
    var plotModel = new PlotModel { Title = "Area Chart Example" };

    // 创建一个 AreaSeries 实例
    var areaSeries = new AreaSeries
    {
        Title = "Series 1",
        Color = OxyColors.Blue,
        StrokeThickness = 2,
        MarkerType = MarkerType.Circle,
        MarkerSize = 4,
        MarkerStroke = OxyColors.White,
        MarkerFill = OxyColors.Blue,
        XAxisKey = "x",
        YAxisKey = "y"
    };

    // 添加数据点
    areaSeries.Points.Add(new DataPoint(0, 10));
    areaSeries.Points.Add(new DataPoint(1, 20));
    areaSeries.Points.Add(new DataPoint(2, 30));
    areaSeries.Points.Add(new DataPoint(3, 25));
    areaSeries.Points.Add(new DataPoint(4, 40));

    // 将系列添加到图表模型中
    plotModel.Series.Add(areaSeries);

    // 配置轴
    plotModel.Axes.Add(new LinearAxis { Position = AxisPosition.Left, Minimum = 0, Maximum = 50, Title = "Value" });
    plotModel.Axes.Add(new LinearAxis { Position = AxisPosition.Bottom, Minimum = 0, Maximum = 4, Title = "Time" });

    return plotModel;
}

areaSeries.Color = OxyColor.FromArgb(255, 0, 0, 255); // 不透明的蓝色

areaSeries.Color = OxyColor.FromArgb(128, 0, 0, 255); // 半透明的蓝色