How do I remove the grey background for dashed lines in a dojo line chart?

http://stackoverflow.com/questions/12671780/how-do-i-remove-the-grey-background-for-dashed-lines-in-a-dojo-line-chart

HTML

<div id="test-chart"></div>

JavaScript

require(["dojox/charting/Chart2D", "dojox/charting/themes/Julie", "dojo/domReady!"
], function(Chart2D, Theme) {
    
    var xChart = new Chart2D("test-chart");
    xChart.setTheme(Theme);
    xChart.addAxis("x");
    xChart.addPlot("default", {type: "Lines"});

    xChart.addSeries("xscsd", [0,0,0,0,0,0],
                     {stroke: {color: "red", width: 1.5, style:"Dot"},
                         outline: null });

    xChart.render();
});