works for me
var cubeMaterial = new THREE.MeshNormalMaterial(cubeMaterials);
Out of curiosity, what revision of three.js are you using?
UPDATE:
It is a very old version, the THREE.MeshFaceMaterial is long outdated.
Your program code looks quite complicated for a three.js beginner. Are you working from a template?
Take a look at the example ColorIndividualFaces from the Collection of examples from discourse.threejs.org.