I’ve enhanced the official glTF example with raycasting so you can actually select the model on click. The code then chances the diffuse color to a random value. The important code is:
var intersects = raycaster.intersectObject(scene, true);
if (intersects.length > 0) {
var object = intersects[0].object;
object.material.color.set( Math.random() * 0xffffff );
}