Green and Amber screens
The mention of green screens reminded me of the early PC days when the monitor was monochrome, and either green or amber for upmarket CAD systems (Hercules graphic cards anyone?). I remember my CAD operator walking into my office and cheerfully sat down with a fresh coffee, saying that his screen just died, and therefore could do no more work until I bought him a new one. After assuring me he'd done nothing to cause the fault except tidy his desk off I went to have a look. Power LED? Check. Computer on? Check. Cables connected? Check. Keyboard pushed right under the monitor, touching the control knobs ... Ah! Restoring the brightness and contrast levels to a central position soon wiped the grin of the smug git's face ...