scaffoldBackgroundColor属性可以设置MaterialApp的背景颜色
使用示例：

return MaterialApp(
      theme: ThemeData(
        primaryColor: Colors.indigo,
        dividerColor: Color(0xFFEFEFEF),
        scaffoldBackgroundColor: Colors.white,
        textTheme: TextTheme(bodyText1: TextStyle(color: Colors.black87)),
      ),
      home: Scaffold(
        body: Stack(
          fit: StackFit.expand,
          children:[
          ]
        ),
      ),
);