材质控制：material

var redTube = viewer.entities.add({
    name : 'Red tube with rounded corners',
    polylineVolume : {
        positions : Cesium.Cartesian3.fromDegreesArray([-85.0, 32.0,-85.0, 36.0,-89.0, 36.0]),
        shape : computeCircle(6000.0),
        //颜色回调
        material : new Cesium.ColorMaterialProperty(new Cesium.CallbackProperty(function() { 
        return Cesium.Color.fromRandom({
            minimumRed : 0.75,
            minimumGreen : 0.75,
            minimumBlue : 0.75,
            alpha : 1.0
        });

        }, false))
    }
});