Desafio de Tela

tomei a liberdade de usar a documentação e incrementar uma APPBAR

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('Desafios Constantes')),
        body: Center(
          child: Container(
            color: Colors.black,
            child: Column(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: [
                const Column(),
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceAround,
                  crossAxisAlignment: CrossAxisAlignment.center,
                  children: [
                    Container(
                      width: 100,
                      height: 100,
                      color: Colors.red,
                    ),
                    Container(
                      width: 100,
                      height: 100,
                      color: Colors.orange,
                    ),
                    Container(
                      width: 100,
                      height: 100,
                      color: Colors.yellow,
                    )
                  ],
                ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceAround,
                  crossAxisAlignment: CrossAxisAlignment.center,
                  children: [
                    Container(
                      width: 100,
                      height: 100,
                      color: Colors.green,
                    ),
                    Container(
                      width: 100,
                      height: 100,
                      color: Colors.blueAccent,
                    ),
                    Container(
                      width: 100,
                      height: 100,
                      color: Colors.blue,
                    )
                  ],
                ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceAround,
                  crossAxisAlignment: CrossAxisAlignment.center,
                  children: [
                    Container(
                      width: 100,
                      height: 100,
                      color: Colors.purple,
                    ),
                    Container(
                      width: 100,
                      height: 100,
                      color: Colors.pinkAccent,
                    ),
                    Container(
                      width: 100,
                      height: 100,
                      color: Colors.white,
                    )
                  ],
                )
              ],
            ),
          ),
        ),
      ),
    );
  }
}