ThemeData.dart

ThemeData(
  primarySwatch: Colors.pink,
  primaryColor: const Color(0xFFe91e63),
  accentColor: const Color(0xFFe91e63),
  canvasColor: const Color(0xFFfafafa),
  fontFamily: 'Roboto',
),

// Usage
return new MaterialApp(
  title: 'Generated App',
    theme: new ThemeData(
    primarySwatch: Colors.pink,
    primaryColor: const Color(0xFFe91e63),
    accentColor: const Color(0xFFe91e63),
    canvasColor: const Color(0xFFfafafa),  
    fontFamily: 'Roboto',
  ),
  home: new MyHomePage(),
);

// References
https://docs.flutter.io/flutter/material/ThemeData-class.html
https://flutterbyexample.com/flutter-theme-class/
https://flutter.io/docs/cookbook/design/themes