Charts 如何删除dojo折线图中虚线的灰色背景？

我用虚线和虚线在Dojo中创建了一个图表。 除了虚线的背景是灰色外，一切都很好

如何删除线条的灰色背景

var xChart = new dojox.charting.Chart2D("test-chart");
xChart.setTheme(dojox.charting.themes.Julie);
xChart.addAxis("x");
xChart.addPlot("default", {type: "Lines"});

xChart.addSeries("xscsd", [2,3,5,5,23,1,6],
   {stroke: {color: "red", width: 1.5, style:"Dot"}});

xChart.render();

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默认主题定义灰色轮廓。添加系列时，用null覆盖大纲

xChart.addSeries("xscsd", [2,3,5,5,23,1,6],
                 {stroke: {color: "red", width: 1.5, style:"Dot"},
                     outline: null });