PLACE TRANSPARENT BLOCK                                            <Alt>+Q

  This operation is very similar to the PLACE BLOCK command except that it
  allows you to make a certain colour "transparent" when placing the data.
  Basically, what this means is that any solid blocks (either a space or the
  block character '#') that appear the same colour as the current text
  colour will not be drawn to the screen.

  Since in most cases you would probably want to interpret black as your
  "transparent" colour, it is generally a good idea to set your text colour
  to black before invoking this operation.