code: def []=(x, y, color)
  			check_coords(x, y)
  			@pixels[x][y] = color
  			@hat[map_coords(x, y)] = color
  		end
docs: Set given pixel identified by +x+, +y+ to +color+
  
   See +set+ for a method that takes individual +r+, +g+, +b+
   components.
  
   You still have to call +show+ to make the changes visible.