登录页面优化 review by 盖剑秋

@@ -155,13 +155,12 @@ var styles = StyleSheet.create({
   button: {
       marginLeft: 20,
       marginRight: 20,
-      backgroundColor: '#ffffff',
-      opacity:0.5,
+      backgroundColor: '#b3b3b3',
       borderWidth:0,
       borderRadius:5,
   },
   buttonText: {
-      color: 'black',
+      color: '#ffffff',
       fontSize: 18,
   },
   buttonDelete: {