Segue meu código de solução do Creeper.

<canvas width="600" height="400"></canvas>

<script>
    function blackLabel() {
        pincel.fillStyle =     'black';
    }

    var tela = document.querySelector('canvas');
    var pincel = tela.getContext('2d');

    pincel.fillStyle = 'white';
    pincel.fillRect(0,0,600,400);


    pincel.fillStyle = 'darkgreen';
    pincel.fillRect(200, 50, 350,300);

    blackLabel();
    pincel.fillRect(250, 100, 90, 90);
    pincel.fillRect(400, 100, 90, 90);

    pincel.fillRect(340, 190, 60, 100);

    pincel.fillRect(300, 250, 40,100);
    pincel.fillRect(400, 250, 40,100);
</script>