"So no-one here has ever seen them before ...?" The essential components of a farce haven't changed much over the years, have they!?

Obviously the thick black line around Eric in the last panel on this page must have been an attempt to stop all the shades of blue ballpoint from merging into one and rendering him invisible.

Or it could have been an attempt to mimic the effect of early blue-screen SFX but somehow that doesn't seem very likely!