减缓CAGradientLayer动画

我想制作一个三色渐变的动画 慢速地 .

我有一个习惯 UIView 像这样:

class MyView: UIView, CAAnimationDelegate {

  lazy var gradientLayer: CAGradientLayer = {
        let l = CAGradientLayer()
        l.frame = self.frame
        l.colors = self.colors
        l.startPoint = CGPoint(x: 0, y: 0)
        l.endPoint = CGPoint(x: 1, y: 0)
        l.mask = self.textLayer
        return l
    }()

    lazy var textLayer: CATextLayer = {
        let l = CATextLayer()
        l.frame = self.frame
        l.string = "test".uppercased()
        l.fontSize = 23
        return l
    }()

    var colors: [CGColor] =  [
            UIColor.red.cgColor,
            UIColor.purple.cgColor,
            UIColor.blue.cgColor
            ]

    init() {
    ...
    self.layer.addSublayer(gradientLayer)

    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func animate() {

      var newColors = colors
      let lastColor: CGColor = newColors.last!
      newColors.removeLast()
      newColors.insert(lastColor, at: 0)

      colors: newColors
      gradientLayer.colors = newColors

      let a = CABasicAnimation(keyPath:"colors")
      a.toValue = newColors
      a.duration = 0.1
      a.isRemovedOnCompletion = true
      a.fillMode = kCAFillModeForwards
      a.delegate = self

      gradientLayer.add(a, forKey:"animateGradient")

    }

    func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {

          animate()
    }

}

这是可行的,但速度非常快。我怎样才能减缓动画的速度,而不让它变得阻塞? 我必须给这个添加几百种颜色吗 colors 数组,使其有足够的循环通过?