Cuadrado con líneas

size(200,200);
background(12,150,100);

stroke(300,0,0);
line(20,20,20,180);

stroke(0,300,0);
line(20,180,180,180);

stroke(300,0,300);
line(180,180,180,20);

stroke(300,300,0);
line(20,20,180,20);