1.primarySwatch 和primaryColor
这个属性设置导航栏颜色

 Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'MyApp',
        theme: ThemeData(
        // primarySwatch 和primaryColor
        primaryColor: Colors.white,
      ),
      home: new BottomNavigationWidget(),
    );

使用primaryColor可以COlors.white,使用primarySwatch不可以设置白色.(具体原因稍后更新)

2.ThemeData与MaterialApp关系
当你在main.dart里面设置了MaterialApp了,那就不需要在其他的界面里面return MaterialApp了,只需要return Scaffold就ok了,如下(具体原因稍后更新)
main.dart

import 'package:flutter/material.dart';
import 'index/index.dart';
void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'MyApp',
        theme: ThemeData(
        // primarySwatch 和primaryColor
        primaryColor: Colors.white,
      ),
      home: new BottomNavigationWidget(),
    );
  }
}

home.main

import 'package:flutter/material.dart';

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return  new Scaffold(
        appBar: new AppBar(
          title: new Text('首页'),
        ),
        body: new Center(
          child: new Text('首页'),
        ),
    );
  }
}