Here is a comparison of the effects of the highlighting change:
The lines prefixed %7 and %8 and in between, show the output is now in grey, and input highlighting is now greenish.
The original "1, 6, 3, 4, 5, 2, 3" profile known as lightbg is reactivated briefly, so it can be compared again.
Making the change permanent on Debian by:
and changing which lines are commented out, results in the top of my
/etc/gprcfile looking like this:
So now when I start up Pari/GP my highlighting is set okay from the outset:
Notes and further reading:
If you want a lighter alternative to emacs on your system, then zile is a lightweight alternative that supports basic editing. Alternatively your system default editor is probably already chosen and use that.
The pari/GP command ...
... can be used interactively if you do not wish to make the change permanent.
darkbg abbreviated to just 'd' should work.