Add constants for material colors and shadows

sky/examples/fn/widgets/floating_action_button.dart

 part of widgets;
 
 class FloatingActionButton extends MaterialComponent {
   // TODO(rafaelw): Ganesh has problems with box shadows
   // box-shadow: 0 10px 20px rgba(0,0,0,0.19), 0 6px 6px rgba(0,0,0,0.23);
 
   static final Style _style = new Style('''
     position: absolute;
     bottom: 16px;
     right: 16px;
     z-index: 5;
     transform: translateX(0);
     width: 56px;
     height: 56px;
-    background-color: #F44336;
+    background-color: ${Red[500]};
     color: white;
     border-radius: 28px;'''
   );
   static final Style _clipStyle = new Style('''
     transform: translateX(0);
     position: absolute;
     display: flex;
     justify-content: center;
     align-items: center;
     top: 0;
@@ skipping 18 matching lines @@
       children: [
         new Container(
           key: "Clip",
           style: _clipStyle,
           children: children
         )
       ]
     );
   }
 }