Bandeiras que são geradas aleatoriamente, mas não repetem a cor

import 'dart:math';

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'exercicio2',
      theme: ThemeData(primarySwatch: Colors.red),
      home: Scaffold(
        appBar: AppBar(
            title: const Text('exercicio2'),
            backgroundColor: Colors.red.shade300),
        body: Container(
            alignment: AlignmentDirectional.topCenter,
            color: Colors.red.shade100,
            padding: const EdgeInsets.fromLTRB(0, 25, 0, 25),
            child: ListView(
              children: [
                Flag(colors: [
                  returnColor(Random().nextInt(2)),
                  returnColor(Random().nextInt(2) + 2),
                  returnColor(Random().nextInt(2) + 4)
                ]),
                Flag(colors: [
                  returnColor(Random().nextInt(2)),
                  returnColor(Random().nextInt(2) + 2),
                  returnColor(Random().nextInt(2) + 4)
                ]),
                Flag(colors: [
                  returnColor(Random().nextInt(2)),
                  returnColor(Random().nextInt(2) + 2),
                  returnColor(Random().nextInt(2) + 4)
                ]),
                Flag(colors: [
                  returnColor(Random().nextInt(2)),
                  returnColor(Random().nextInt(2) + 2),
                  returnColor(Random().nextInt(2) + 4)
                ]),
                Flag(colors: [
                  returnColor(Random().nextInt(2)),
                  returnColor(Random().nextInt(2) + 2),
                  returnColor(Random().nextInt(2) + 4)
                ]),
              ],
            )),
      ),
    );
  }
}

class Flag extends StatefulWidget {
  List<Color> colors;

  Flag({required this.colors, Key? key}) : super(key: key);

  @override
  State<Flag> createState() => _FlagState();
}

class _FlagState extends State<Flag> {
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(10),
      child: Column(
        children: renderContainers(widget.colors),
      ),
    );
  }
}

Container doContainer(Color color) {
  return Container(
    width: 200,
    height: 40,
    color: color,
  );
}

List<Container> renderContainers(List<Color> list) {
  List<Container> containers = [];
  for (var color in list) {
    containers.add(doContainer(color));
  }
  return containers;
}

Color returnColor(int i) {
  print(i);
  if (i == 0) {
    return Colors.blue;
  } else if (i == 1) {
    return Colors.amber;
  } else if (i == 2) {
    return Colors.green;
  } else if (i == 3) {
    return Colors.red;
  } else if (i == 4) {
    return Colors.deepPurple;
  } else {
    return Colors.white;
  }
}