Swift tvos：更改TVCaptionButtonView的聚焦颜色

如何更改tvos swift TVCaptionButtonView选择的默认白色

我试图以这种方式改变

class MyTVCaptionButtonView: TVCaptionButtonView {
    override func didUpdateFocus(in context: UIFocusUpdateContext, with coordinator: UIFocusAnimationCoordinator) {
        let highlight = context.nextFocusedView == self
        print("highlighted \(highlight)")
        self.backgroundColor = highlight ? .red : .green
        self.contentView.backgroundColor = highlight ? .yellow : .black
    }
}

但当按钮聚焦时，背景仍然是白色的