Synopsis:
set highlight [reset | plain | light | dark | off]
Set whether we use terminal highlighting; Permissable values are:
- plain
- 
no terminal highlighting 
- off
- 
same as plain 
- light
- 
terminal background is light; this is the default 
- dark
- 
terminal background is dark or light forgeground text 
If the first argument is reset, we clear any existing color formatting and recolor all source code output.
Examples:
set highlight off   # no highlight
set highlight plain # same as above
set highlight dark  # terminal has dark background
set highlight light # terminal has light background
set highlight       # same as above
set highlight reset light # clear source-code cache and
                          # set for light background
set highlight reset # clear source-code cache