你如何明确动画CALayer的backgroundColor动画？

let animation = CABasicAnimation(keyPath: "backgroundColor")
animation.fromValue = UIColor.red.cgColor
animation.toValue = UIColor.blue.cgColor
animation.duration = 2.0
layer.add(animation, forKey: "backgroundColorAnimation")

layer.actions = ["backgroundColor": NSNull()]

class MyLayerDelegate: NSObject, CAAnimationDelegate {
    func animationDidStart(_ anim: CAAnimation) {
        print("Animation started")
    }
    
    func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
        print("Animation stopped")
    }
}

let delegate = MyLayerDelegate()
layer.delegate = delegate

layer.speed = 2.0