Thanks for reporting this. Following workaround (for flex sdk 4.6 regression) will be added in the next release of the viewer..Add to InfoColumnChartWidget.mxml following funtions:
private function basewidget_preinitializeHandler(event:FlexEvent):void
            {
                // work-around for 4.6 regression
                copyStyleFromParent("mx.charts.chartClasses.ChartBase");
                copyStyleFromParent("mx.charts.chartClasses.CartesianChart");
                copyStyleFromParent("mx.charts.chartClasses.PolarChart");
                copyStyleFromParent("mx.charts.BarChart");
                copyStyleFromParent("mx.charts.ColumnChart");
                copyStyleFromParent("mx.charts.LineChart");
                copyStyleFromParent("mx.charts.PieChart");
                copyStyleFromParent("mx.charts.AxisRenderer");
                copyStyleFromParent(".blockCategoryAxis");
                copyStyleFromParent(".blockNumericAxis");
                copyStyleFromParent(".linedNumericAxis");
                copyStyleFromParent(".dashedNumericAxis");
                copyStyleFromParent(".dashedCategoryAxis");
                copyStyleFromParent(".hangingCategoryAxis");
                copyStyleFromParent("mx.charts.GridLines");
                copyStyleFromParent(".horizontalGridLines");
                copyStyleFromParent("mx.charts.series.BarSeries");
                copyStyleFromParent("mx.charts.series.ColumnSeries");
                copyStyleFromParent("mx.charts.series.LineSeries");
                copyStyleFromParent("mx.charts.series.PieSeries");
            }
            
            private function copyStyleFromParent(selector:String):void
            {
                var chartBaseStyle:CSSStyleDeclaration = styleManager.getStyleDeclaration(selector);
                if (!chartBaseStyle && styleManager.parent)
                {
                    var parentStyle:CSSStyleDeclaration = styleManager.parent.getStyleDeclaration(selector);
                    if (parentStyle)
                    {
                        styleManager.setStyleDeclaration(selector, parentStyle, false);
                    }
                }
            }and update following:<viewer:BaseWidget xmlns:fx="http://ns.adobe.com/mxml/2009"
                   xmlns:s="library://ns.adobe.com/flex/spark"
                   xmlns:mx="library://ns.adobe.com/flex/mx"
                   xmlns:viewer="com.esri.viewer.*"
                   creationComplete="init()"
                   preinitialize="basewidget_preinitializeHandler(event)"
                   implements="com.esri.viewer.IInfowindowTemplate">