// Add debugShowCheckedModeBanner: false to your Material
return new MaterialApp(
	debugShowCheckedModeBanner: false,
    theme: new ThemeData(
      primarySwatch: Colors.green,
    ),
    //...
);

MaterialApp(
  debugShowCheckedModeBanner: false,
)

MaterialApp(
  home: MyHomePage(),
  debugShowCheckedModeBanner: false,
);

debugShowCheckedModeBanner: false,
return new MaterialApp(
    debugShowCheckedModeBanner: false,
    home: new Column(
        ...
    )
); 

MaterialApp(
 debugShowCheckedModeBanner: false
)