Resolução do exercício

Olá, meu código ficou desta forma:

      home: Column(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        children: [
          Row(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            children: [
              Container(color: Colors.red, height: 100, width: 100,),
              Container(color: Colors.orange, height: 100, width: 100,),
              Container(color: Colors.yellow, height: 100, width: 100,)
            ],
          ),
          Row(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            children: [
              Container(color: Colors.green, height: 100, width: 100,),
              Container(color: Colors.cyan, height: 100, width: 100,),
              Container(color: Colors.blue, height: 100, width: 100,)
            ],
          ),
          Row(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            children: [
              Container(color: Colors.purple, height: 100, width: 100,),
              Container(color: Colors.pink, height: 100, width: 100,),
              Container(color: Colors.white, height: 100, width: 100,)
            ],
          )
        ],
      ),

Resultando nesta tela: