How to do it...

To implement this functionality, follow these steps:

1. Add a new file to your project, calling it navigation_dialog.dart.
2. Add the following code to the navigation_dialog.dart file: 

import 'package:flutter/material.dart';

class NavigationDialog extends StatefulWidget {
  @override
  _NavigationDialogState createState() => _NavigationDialogState();
}

class _NavigationDialogState extends State<NavigationDialog> {
  Color color = Colors.blue[700];
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        backgroundColor: color,
        appBar: AppBar(
          title: Text('Navigation Dialog Screen'),
        ),
        body: Center(
            child: ElevatedButton(
              child: Text('Change Color'),
              onPressed: () {
              }),
          ),
        );
  }

3. Now create the asynchronous method that will return the chosen color, calling it showColorDialog, and marking it as async:

 _showColorDialog(BuildContext...