Swift transposed version of a different color approach on all sides of a `SCNBox` (https://stackoverflow.com/a/27509866/856336)

SCNBox_Different_Color_Sides.swift

/// Generate `SCNMaterial` that is the specified color
func material(withColor color : UIColor) -> SCNMaterial {
    let material = SCNMaterial();
    material.diffuse.contents = color
    material.locksAmbientWithDiffuse = true
    return material
}

let greenMaterial = material(withColor: UIColor.green)
let redMaterial = material(withColor: UIColor.red)
let blueMaterial = material(withColor: UIColor.blue)
let yellowMaterial = material(withColor: UIColor.yellow)
let purpleMaterial = material(withColor: UIColor.purple)
let magentaMaterial = material(withColor: UIColor.magenta)

cube.materials = [greenMaterial, redMaterial, blueMaterial, yellowMaterial, purpleMaterial, magentaMaterial];