Refactoring to support dark theme better

sky/sdk/example/widgets/styled_text.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'package:sky/painting/text_style.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/rendering/sky_binding.dart';
 import 'package:sky/theme/colors.dart' as colors;
 import 'package:sky/widgets/basic.dart';
@@ skipping 88 matching lines @@
           alignItems: FlexAlignItems.flexStart
         )
       );
 
     Listener interactiveBody = new Listener(
       child: body,
       onPointerDown: toggleToTextFunction
     );
 
     return new Theme(
-      data: new ThemeData.light(primary: colors.Blue, darkToolbar: true),
+      data: new ThemeData.light(),
       child: new Scaffold(
         body: new Material(
           color: colors.Grey[50],
           child: interactiveBody
         ),
         toolbar: new ToolBar(
           center: new Text('Hal and Dave')
         )
       )
     );
   }
 }
 
 void main() {
   runApp(new StyledTextApp());
   SkyBinding.instance.onFrame = () {
     // uncomment this for debugging:
     // SkyBinding.instance.debugDumpRenderTree();
   };
 }