docs: def paint_cube(self, x, y):
          """
          Paints a cube at a certain position a color.
  
          Parameters
          ----------
          x: int
              Horizontal position of the upper left corner of the cube.
          y: int
              Vertical position of the upper left corner of the cube.
  
          """
          # get the color
          color = self.next_color()
          # calculate the position
          cube_pos = [x, y, x + self.cube_size, y + self.cube_size]
          # draw the cube
          draw = ImageDraw.Draw(im=self.image)
          draw.rectangle(xy=cube_pos, fill=color)