circle primitive renders oddly

I don't see a way to post a screen shot so i guess it you want to see what I'm talking about you have to go to my test site and look at it.

Zoom into Western NY State and look at the two overlapping circles. The one on the left is a primitive and the one on the right is not.

Why doesn't the primitive render a uniform green? There is a strange pattern in it.

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

var entity = viewer.entities.add({
           position: Cesium.Cartesian3.fromDegrees(-78.2221, 42.9898),
           ellipse: {
                semiMinorAxis: 50000.0,
                semiMajorAxis: 50000.0,
                material: Cesium.Color.GREEN.withAlpha(0.5),

var ellipse = entity.ellipse;

var scene = viewer.scene;
var instances = ;
        instances.push(new Cesium.GeometryInstance({
            geometry: new Cesium.CircleGeometry({
                center: Cesium.Cartesian3.fromDegrees(-78.8784, 42.8864),
                radius: 50000.0
            attributes: {
                color: Cesium.ColorGeometryInstanceAttribute.fromColor(Cesium.Color.fromAlpha(Cesium.Color.GREEN, 0.5))

You need to pass the correct vertexFormat to the CircleGeometry constructor. Here is an example:

new Cesium.CircleGeometry({
center: Cesium.Cartesian3.fromDegrees(-78.8784, 42.8864),
radius: 50000.0,
vertexFormat : Cesium.PerInstanceColorAppearance.VERTEX_FORMAT




Thank you!