Cant quite only color the external faces of a rubiks cube

Questions
,
1

Im trying to create a rubiks cube and im having kinda stupid problem.
Basically i only want to color the showing faces of the “big cube” but all i am getting so far is all the 27 “mini cubes” colored in ALL the faces and thats kinda f*ing my head.
Here’s the code im using to color the mini cubes:

   for (var i = 0; i < this.geometry.faces.length; i += 2){       
     var color = colors[indiceCor++] //color of each face 
     this.geometry.faces[i].color.set(color); //triangle 1
     this.geometry.faces[i+1].color.set(color);//triangle 2      
    }
    // cubes material
    this.material = new THREE.MeshBasicMaterial({
        vertexColors: true 
    }); 

    //creating all the cubes
    for (let x = -1; x < 2; x++) {
        
        for (let y = -1; y < 2; y++) {
            
            for (let z = -1; z < 2; z++) {
                
                if ((x === 0) && (y === 0) && (z === 0)) {
                    continue;
                }
    let cube =new THREE.Mesh(this.geometry,this.material);
                cube.position.x = x;
                cube.position.y = y;
                cube.position.z = z;
                this.scene.add(cube)
                this.cubes.push(cube);
            }
        }
    }