Cesium example of coloring a model loaded with the Entity API

EntityModelColor.js

var viewer = new Cesium.Viewer('cesiumContainer', {
    infoBox : false,
    selectionIndicator : false
});

var entity = viewer.entities.add({
    position : Cesium.Cartesian3.fromDegrees(-123, 44, 10),
    model : {
        uri : '../../../Specs/Data/Models/Box/CesiumBoxTest.gltf',
        minimumPixelSize : 128
    }
});
viewer.zoomTo(entity, new Cesium.HeadingPitchRange(Math.PI / 4, -Math.PI / 4, 3));

//Change color on mouse over.  This relies on the fact that given a primitive,
//you can retrieve an associted en
var lastColor;
var lastPick;
var handler = new Cesium.ScreenSpaceEventHandler(viewer.scene.canvas);
handler.setInputAction(function(movement) {
    var primitive;
    var pickedObject = viewer.scene.pick(movement.endPosition);
    if (pickedObject) {
        primitive = pickedObject.primitive;
        if (pickedObject !== lastPick && primitive instanceof Cesium.Model) {

            //We don't use the entity here, but if you need to color based on 
            //some entity property, you can get to that data it here.
            var entity = primitive.id;
            
            var material = primitive.getMaterial('Red');
            lastColor = material.getValue('diffuse').clone();
            material.setValue('diffuse', Cesium.Cartesian4.fromColor(Cesium.Color.BLUE));
            lastPick = pickedObject;
        }
    } else if (lastPick) {
        primitive = lastPick.primitive;
        var material = primitive.getMaterial('Red');
        material.setValue('diffuse', lastColor);
        lastPick = undefined;
    }
}, Cesium.ScreenSpaceEventType.MOUSE_MOVE);

//Ability to look up the Model associated with an entity
function getModelForEntity(entity) {
    var primitives = viewer.scene.primitives;
    for (var i = 0; i < primitives.length; i++) {
        var primitive = primitives.get(i);
        if (primitive instanceof Cesium.Model && primitive.id === entity) {
            return primitive;
        }
    }
};

//Makes an entity model a random color.
Sandcastle.addToolbarButton('Make random color', function() {
    var model = getModelForEntity(entity);
    if (model) {
        var material = model.getMaterial('Red');
        material.setValue('diffuse', Cesium.Cartesian4.fromColor(Cesium.Color.fromRandom()));
    }
});