Flutterでアプリ開発・画面UIのテーマを決める

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

The following _TypeError was thrown building MyApp(dirty):
type 'Color' is not a subtype of type 'MaterialColor'
The relevant error-causing widget was:
MyApp file:///Users/tomoakihirosawa/Documents/develop/my_app_name/lib/main.dart:4:10
When the exception was thrown, this was the stack:
0 MyApp.build (package:my_app_name/main.dart:14:31)
1 StatelessElement.build (package:flutter/src/widgets/framework.dart:4576:28)
2 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4502:15)
3 Element.rebuild (package:flutter/src/widgets/framework.dart:4218:5)
4 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2627:33)
…

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData.dark(),　　＜ーーこれだけ
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primaryColor: Color(0xFF00acc1),
        primaryColorLight: Color(0xFF5ddef4),
        primaryColorDark: Color(0xFF007c91),
        primaryTextTheme: TextTheme(headline6: TextStyle(color: Color(0xFF000000))),
        floatingActionButtonTheme: FloatingActionButtonThemeData(backgroundColor: Color(0xFF00acc1)),
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}