Simulator crashing when I press the fun fact button

@IBOutlet weak var funFactLabel: UILabel!

let factBook = FactBook()
let colorWheel = ColorWheel()

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    funFactLabel.text = factBook.randomFact()
}

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

@IBAction func showFunFact() {
    view.backgroundColor = colorWheel.randomColor()
    funFactLabel.text = factBook.randomFact()
}

let factsArray = [
    "Ants stretch when they wake up in the morning.",
    "Ostriches can run faster than horses.",
    "Olympic gold medals are actually made mostly of silver.",
    "You are born with 300 bones; by the time you are an adult you will have 206.",
    "It takes about 8 minutes for light from the Sun to reach Earth.",
    "Some bamboo plants can grow almost a meter in just one day.",
    "The state of Florida is bigger than England.",
    "Some penguins can leap 2-3 meters out of the water.",
    "On average, it takes 66 days to form a new habit.",
    "Mammoths still walked the earth when the Great Pyramid was being built."
]

func randomFact() -> String {
    var unsignedArrayCount = UInt32(factsArray.count)
    var unsignedRandomNumber = arc4random_uniform(unsignedArrayCount)
    var randomNumber = Int(unsignedRandomNumber)

    return factsArray[randomNumber]
}

let colorsArray = [
    UIColor(red: 90/255.0, green: 187/255.0, blue: 181/255.0, alpha: 1.0),  // teal color
    UIColor(red: 222/255.0, green: 171/255.0, blue: 66/255.0, alpha: 1.0),  // yellow color
    UIColor(red: 223/255.0, green: 86/255.0, blue: 94/255.0, alpha: 1.0),   // red color
    UIColor(red: 239/255.0, green: 130/255.0, blue: 100/255.0, alpha: 1.0), // orange color
    UIColor(red: 77/255.0, green: 75/255.0, blue: 82/255.0, alpha: 1.0),    // dark color
    UIColor(red: 105/255.0, green: 94/255.0, blue: 133/255.0, alpha: 1.0),  // purple color
    UIColor(red: 85/255.0, green: 176/255.0, blue: 112/255.0, alpha: 1.0),  // green color
]

func randomColor() -> UIColor {
    var unsignedArrayCount = UInt32(colorsArray.count)
    var unsignedRandomNumber = arc4random_uniform(unsignedArrayCount)
    var randomNumber = Int(unsignedRandomNumber)

    return colorsArray[randomNumber]
}