title: What is the proper way of using ThemeData copyWith in flutter MaterialApp widget?
body: <p>I was trying to change the <code>accentColor</code> after copying the <code>ThemeData.light()</code>, then I have this sample screen with a <code>FloatingActionButton</code></p>
  
  <pre><code>class Sample extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
      return Scaffold(
        floatingActionButton: FloatingActionButton(
          onPressed: () {},
          child: Icon(Icons.add),
        ),
       )}}
  </code></pre>
  
  <p>Then in the main widget in <code>main.dart</code> to call <code>runApp</code>, if I set the <code>ThemeData</code> for the <code>MaterialApp</code> widget like this, The <code>FloatingActionButton</code> will have a color of orange.</p>
  
  <pre><code>theme: ThemeData(
    accentColor: Colors.orange
  )
  </code></pre>
  
  <p>but if I tried to inherit the color from the <code>Themedata.light().copyWith</code>, the <code>FloatingActionButton</code> will still have the color blue from the light theme.</p>
  
  <pre><code>theme: ThemeData.light().copyWith(
    accentColor: Colors.orange
  )
  </code></pre>
  
  <p>I was expecting the <code>FloatingActionButton</code> should have the orange color, because It inherit the <code>light</code> theme and override the <code>accentColor</code>.</p>