tvos：更改 UIButton 的焦点颜色

问：

如何更改tvos swift UI的默认白色布顿焦点选择？

override func didUpdateFocus(in context: UIFocusUpdateContext, with coordinator: UIFocusAnimationCoordinator) {
    if let nextFocusedView = context.nextFocusedView {
        playAllOutlet.backgroundColor  = UIColor.red
        shuffleBtnOutlet.backgroundColor = UIColor.green
    
    }
    
    if let previousFocusView = context.previouslyFocusedView {
           playAllOutlet.backgroundColor  = UIColor.red
        shuffleBtnOutlet.backgroundColor = UIColor.green
    }
}

但是按钮聚焦时的背景仍然是白色的