Flutter: Change RaisedButton color dynamically in onPressed function

main.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List<Zone> zones = [
    Zone('zone1', true, color: Colors.blue),
    Zone('zone1', false, color: Colors.blue),
    Zone('zone1', true, color: Colors.blue),
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
          child: Wrap(
        children: _createButton(context, zones),
      )),
    );
  }

  List<Widget> _createButton(BuildContext context, List<Zone> zones) {
    return zones.map((Zone zone) {
      return RaisedButton(
        onPressed: () {
          setState(() {
            if (!zone.isSelected) {
              zone.color = Colors.white;
            }
          });
        },
        color: zone.color ??= Theme.of(context).primaryColor,
        child: Text(zone.text),
      );
    }).toList();
  }
}

class Zone {
  String text;
  bool isSelected;
  Color color;

  Zone(this.text, this.isSelected, {this.color});
}