title: RichText does not style text as expected
body: <p>Just created a project with:</p>
  
  <pre><code>&gt; flutter create simple
  </code></pre>
  
  <p>and added a <code>RichText</code> widget,
  but the result it is not what I expect: a default styled text with only the word bold in bold.
  On my android device I get instead:</p>
  
  <p><a href="https://i.stack.imgur.com/DYzrn.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/DYzrn.jpg" alt="enter image description here"></a></p>
  
  <p>full main.dart:</p>
  
  <pre><code>import 'package:flutter/material.dart';
  
  void main() =&gt; runApp(new MyApp());
  
  class MyApp extends StatelessWidget {
    // This widget is the root of your application.
    @override
    Widget build(BuildContext context) {
      return new MaterialApp(
        title: 'Flutter Demo',
        theme: new ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: new MyHomePage(title: 'Flutter Demo Home Page'),
      );
    }
  }
  
  class MyHomePage extends StatefulWidget {
    MyHomePage({Key key, this.title}) : super(key: key);
  
    final String title;
  
    @override
    _MyHomePageState createState() =&gt; new _MyHomePageState();
  }
  
  class _MyHomePageState extends State&lt;MyHomePage&gt; {
    int _counter = 0;
  
    void _incrementCounter() {
      setState(() {
        _counter++;
      });
    }
  
    @override
    Widget build(BuildContext context) {
      return new Scaffold(
        appBar: new AppBar(
          title: new Text(widget.title),
        ),
        body: new Center(
          child: new Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: &lt;Widget&gt;[
              new RichText(
                text: new TextSpan(
                  text: 'Hello ',
                  style: DefaultTextStyle.of(context).style,
                  children: &lt;TextSpan&gt;[
                    new TextSpan(
                        text: 'bold',
                        style: new TextStyle(fontWeight: FontWeight.bold)),
                    new TextSpan(text: ' world!'),
                  ],
                ),
              ),
              new Text(
                'You have pushed the button this many times:',
              ),
              new Text(
                '$_counter',
                style: Theme.of(context).textTheme.display1,
              ),
            ],
          ),
        ),
        floatingActionButton: new FloatingActionButton(
          onPressed: _incrementCounter,
          tooltip: 'Increment',
          child: new Icon(Icons.add),
        ), 
      );
    }
  }
  </code></pre>
  
  <p>What am I missing? From where does it came this "red" theme?</p>