Threejs skydome and Tweenmax

Question

I've been trying to animate the colors of a skydome in threejs with Tweenmax but all my attempts failed.

Does anyone has a clue how to do that? Thanks a lot.

//////// SKYBOX////////
    var vertexShader = document.getElementById('sky-vertex').textContent, fragmentShader = document.getElementById('sky-fragment').textContent;
       var uniforms = {
    topColor: {type: "c", value: new THREE.Color(blue)}, //autour
    bottomColor: {type: "c", value: new THREE.Color(blue)}, //milieu
    offset: {type: "f", value: 30}, 
    exponent: {type: "f", value: 0.18}
};

var elem = document.getElementById('sky-fragment')
var blueFirst =  new THREE.Color( 0x08088A ).getHex();
var blueSecond = new THREE.Color( 0x81F7F3 ).getHex(); 
var blue = TweenMax.fromTo(elem,0.5,{color: blueFirst},{color: blueSecond});

var skyBox = new THREE.Mesh( skyGeometry, skyMaterial );
scene.add( skyBox );