如何在showMenu下改变PopupMenuItem的背景色？

PopupMenuButton(
  onSelected: (value) {
    // 处理选择菜单项后的操作
  },
  itemBuilder: (BuildContext context) {
    return [
      PopupMenuItem(
        value: 1,
        child: Text('菜单项1'),
      ),
      PopupMenuItem(
        value: 2,
        child: Text('菜单项2'),
      ),
    ];
  },
)

class MyPopupMenu extends StatefulWidget {
  @override
  _MyPopupMenuState createState() => _MyPopupMenuState();
}

class _MyPopupMenuState extends State<MyPopupMenu> {
  int selectedValue;

  @override
  Widget build(BuildContext context) {
    return PopupMenuButton(
      onSelected: (value) {
        setState(() {
          selectedValue = value;
        });
      },
      itemBuilder: (BuildContext context) {
        return [
          PopupMenuItem(
            value: 1,
            child: Container(
              color: selectedValue == 1 ? Colors.blue : null,
              child: Text('菜单项1'),
            ),
          ),
          PopupMenuItem(
            value: 2,
            child: Container(
              color: selectedValue == 2 ? Colors.blue : null,
              child: Text('菜单项2'),
            ),
          ),
        ];
      },
    );
  }
}

showMenu(
  context: context,
  position: RelativeRect.fromLTRB(100, 100, 0, 0),
  items: [
    PopupMenuItem(
      child: MyPopupMenu(),
    ),
  ],
);