Entity canvas materials don't behave as expected

[mramato]

In the below code, both polygons end up yellow, rather than one yell and one red.

var viewer = new Cesium.Viewer('cesiumContainer');

var canvas1 = document.createElement('canvas');
canvas1.height = 100;
canvas1.width = 100;
var context = canvas1.getContext('2d');
context.rect(0,0,100,100);
context.fillStyle = 'red';
context.fill();

var canvas2 = document.createElement('canvas');
canvas2.height = 100;
canvas2.width = 100;
var context2 = canvas2.getContext('2d');
context2.rect(0,0,100,100);
context2.fillStyle = 'yellow';
context2.fill();

viewer.entities.add({
    polygon : {
        hierarchy : Cesium.Cartesian3.fromDegreesArray([-115.0, 37.0,
                                                        -115.0, 32.0,
                                                        -107.0, 33.0,
                                                        -102.0, 31.0,
                                                        -102.0, 35.0]),
        material : canvas1
    }
});

viewer.entities.add({
    polygon : {
        hierarchy : Cesium.Cartesian3.fromDegreesArray([-30.0, 37.0,
                                                        -20.0, 32.0,
                                                        -10.0, 33.0]),
        material : canvas2
    }
});

viewer.zoomTo(viewer.entities);

[mramato]

Forgot to link to the forum post where this was reported.