$ flutter create <project name>

$ cd <project name>
$ flutter run 

<key>CFBundleDisplayName</key>
<string>EXAMPLE APP</string>  <!-- ←ここを編集  -->

<manifest xmlns:android="http://schemas.android.com/apk/res/android">
    <application
        android:label="EXAMPLE APP" <!-- ←ここを編集 --->
        android:name="${applicationName}"
        android:icon="@mipmap/ic_launcher">

$ flutter pub add flutter_launcher_icons

flutter_launcher_icons:
  android: "launcher_icon"
  ios: true
  image_path: "assets/icon/example.png"

$ flutter pub get
$ flutter pub run flutter_launcher_icons

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Example',
      theme: ThemeData(
        primarySwatch: MaterialColor(0xFFC9A99A),  // これだとエラーが出る．
      ),
      home: new LoginPage(),
    );
  }
}

class MyApp extends StatelessWidget {
  final MaterialColor primaryColor =
      const MaterialColor(0xFFC9A99A, <int, Color>{
    50: Color(0xFFF9F5F3),
    100: Color(0xFFEFE5E1),
    200: Color(0xFFE4D4CD),
    300: Color(0xFFD9C3B8),
    400: Color(0xFFD1B6A9),
    500: Color(0xFFC9A99A), // use this color as primary color of widgets
    600: Color(0xFFC3A292),
    700: Color(0xFFBC9888),
    800: Color(0xFFB58F7E),
    900: Color(0xFFA97E6C),
  });

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Cook Helper',
      theme: ThemeData(
        primarySwatch: primaryColor,
      ),
      home: new LoginPage(),
    );
  }
}

[ERROR:flutter/shell/platform/darwin/graphics/FlutterDarwinContextMetalImpeller.mm(42)] Using the Impeller rendering backend.
[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Binding has not yet been initialized.
The "instance" getter on the ServicesBinding binding mixin is only available once that binding has been initialized.
Typically, this is done by calling "WidgetsFlutterBinding.ensureInitialized()" or "runApp()" (the latter calls the former). Typically this call is done in the "void main()" method. The "ensureInitialized" method is idempotent; calling it multiple times is not harmful. After calling that method, the "instance" getter will return the binding.
In a test, one can call "TestWidgetsFlutterBinding.ensureInitialized()" as the first line in the test's "main()" method to initialize the binding.
If ServicesBinding is a custom binding mixin, there must also be a custom binding class, like WidgetsFlutterBinding, but that mixes in the selected binding, and that is the class that must be constructed before using the "instance" getter.

WidgetsFlutterBinding.ensureInitialized();

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp(
    options: DefaultFirebaseOptions.currentPlatform,
  );
  runApp(const MyApp());
}

ElevatedButton(
  style: ElevatedButton.styleFrom(
    backgroundColor: Colors.red, // background
    foregroundColor: Colors.white, // foreground
  ),
  onPressed: () { },
  child: Text('ElevatedButton with custom foreground/background'),
)

class AuthButton {
  static ButtonStyle style = ElevatedButton.styleFrom(
      backgroundColor: CommonColors.primaryColor,
      foregroundColor: Colors.black);
}

$ flutter pub add gap

TextFormField(
・・・
),
const Gap(50),
// 3行目 ユーザ登録ボタン
ElevatedButton(
・・・
)

bottomNavigationBar: BottomNavigationBar(
    backgroundColor: ・・・　// 　←ここのこと
・・・・
・・・・