import 'package:flutter/material.dart';
import 'dart:math';

class App extends StatefulWidget {
  createState() {
    return Colore();
  }
}

class Colore extends State<App> {
  List colors = [Colors.red, Colors.green, Colors.yellow];
  Random random = new Random();

  int index = 0;

  void changeIndex() {
    setState(() => index = random.nextInt(3));
  }

  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          backgroundColor: Color(Colors.orange),
          title: Text('DisColor'),
        ),
        floatingActionButton: FloatingActionButton(
            child: Icon(Icons.explore),
            onPressed: () {
              changeIndex();
            },
            backgroundColor: Color(Colors.amber),),
        body: Container(
          color: colors[index],
        ),
      ),
    );
  }
}

void main() {
  runApp(App());
}