比较好用的测试方法: 生成随机颜色
static var randomColor: UIColor {// 随机颜色
let red = CGFloat(arc4random() % 256) / 255.0
let green = CGFloat(arc4random() % 256) / 255.0
let blue = CGFloat(arc4random() % 256) / 255.0
let color = UIColor(red: red, green: green, blue: blue, alpha: 1.0)
return color
}
