It is not easy being green (#4606)

examples/flutter_gallery/lib/demo/icons_demo.dart

@@ -34,7 +34,7 @@ class IconsDemoState extends State<IconsDemo> {
     Colors.blueGrey
   ];
 
-  int iconColorIndex = 9; // green
+  int iconColorIndex = 8; // teal
   double iconOpacity = 1.0;
 
   Color get iconColor => iconColorSwatches[iconColorIndex][400];

examples/flutter_gallery/lib/gallery/app.dart

@@ -16,12 +16,12 @@ final Map<String, WidgetBuilder> _kRoutes = new Map<String, WidgetBuilder>.fromI
 
 final ThemeData _kGalleryLightTheme = new ThemeData(
   brightness: Brightness.light,
-  primarySwatch: Colors.green
+  primarySwatch: Colors.teal
 );
 
 final ThemeData _kGalleryDarkTheme = new ThemeData(
   brightness: Brightness.dark,
-  primarySwatch: Colors.green
+  primarySwatch: Colors.teal
 );
 
 class GalleryApp extends StatefulWidget {