I decommented and edited the two lines in /etc/default/grub
which are relative to the colors, as follows
GRUB_COLOR_NORMAL="green/black"
GRUB_COLOR_HIGHLIGHT="light-green/green"
then I've run sudo grub-mkconfig -o /boot/grub/grub.cfg
and reboot. Strangely it seems that only the second line had effect.
On the other hand, when I hit C on GRUB's main screen and get the console, then I can enter, for instance, set color_normal=yellow/blue
and set color_highlight=red/cyan
and verify that both commands had effect (after going back to GRUB's main screen by hitting Esc).
I've also tried to put those two lines just before
if [ x$GRUB_COLOR_NORMAL != x ] && [ x$GRUB_COLOR_HIGHLIGHT != x ] ; then
cat << EOF
set menu_color_normal=$GRUB_COLOR_NORMAL
set menu_color_highlight=$GRUB_COLOR_HIGHLIGHT
EOF
fi
in /etc/grub.d/00_header
, thinking that /etc/default/grub
could be overridden by this latter file, but it still has no effect.