Faça como eu fiz: uma nova tela

Acho que fiz da forma mais simples que dava

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: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: Container(
        color: Colors.black,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceAround,
          children: [
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: [
                Container(
                  color: Colors.red,
                  width: 100,
                  height: 100,
                ),
                Container(
                  color: Colors.orange,
                  width: 100,
                  height: 100,
                ),
                Container(
                  color: Colors.yellow,
                  width: 100,
                  height: 100,
                ),
              ],
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: [
                Container(
                  color: Colors.green,
                  width: 100,
                  height: 100,
                ),
                Container(
                  color: Colors.lightBlueAccent,
                  width: 100,
                  height: 100,
                ),
                Container(
                  color: Colors.blue,
                  width: 100,
                  height: 100,
                ),
              ],
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: [
                Container(
                  color: Colors.purple,
                  width: 100,
                  height: 100,
                ),
                Container(
                  color: Colors.pink,
                  width: 100,
                  height: 100,
                ),
                Container(
                  color: Colors.white,
                  width: 100,
                  height: 100,
                ),
              ],
            ),

          ],
        ),
      ),
    );
  }
}