How do I change the colors of 9 objects after the right object is pressed?

I have 9 buttons/squares that each have a different color. When the right color is pressed, all the buttons should switch colors. For example: if I press the red square, then the colors of the squares should change so that another square becomes red. So far I got

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    var Ctimer = NSTimer.scheduledTimerWithTimeInterval(0.1, target: self, selector: "colors", userInfo: nil, repeats: true)

    B1.backgroundColor = UIColor.blueColor()
    B2.backgroundColor = UIColor.greenColor()
    B3.backgroundColor = UIColor.cyanColor()
    B4.backgroundColor = UIColor.purpleColor()
    B5.backgroundColor = UIColor.redColor()
    B6.backgroundColor = UIColor.brownColor()
    B7.backgroundColor = UIColor.yellowColor()
    B8.backgroundColor = UIColor.orangeColor()
    B9.backgroundColor = UIColor.magentaColor()
}

func colors() {
    var red = CGFloat(drand48())
    var green = CGFloat(drand48())
    var blue = CGFloat(drand48())
    self.view.backgroundColor = UIColor(red: red, green: green, blue: blue, alpha: 1.0)
}

func changeButtonColors(){

    var rand = arc4random_uniform(10)


}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


}

B1, B2, etc are buttons. I am confused as to how I can randomize the change of colors without having to hardcode every possible alternative.