Use the markerType, markerSize, and markerFill attributes to set the style, size, and color of the markers. Use the strokeColor and strokeWidth attributes to set the color and thickness of the connecting lines. Optionally, set fill=true to fill the area enclosed by the series, and use opacity to make it transparent so that other series remain visible. The opacity attribute is a floating point number between 0.0 and 1.0, with 0.0 being fully transparent and 1.0 being fully opaque.
<apex:chart height="530" width="700" legend="true" data="{!data}"> <apex:legend position="left"/> <apex:axis type="Radial" position="radial"> <apex:chartLabel /> </apex:axis> <apex:radarSeries xField="name" yField="data1" tips="true" opacity="0.4"/> <apex:radarSeries xField="name" yField="data2" tips="true" opacity="0.4"/> <apex:radarSeries xField="name" yField="data3" tips="true" markerType="cross" strokeWidth="2" strokeColor="#f33" opacity="0.4"/> </apex:chart>