For completeness:

As separate lines:

 $menu->selection_bgcolor("GREEN");
 $menu->selection_fgcolor("YELLOW");
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Inside the constructor:

my $menu = Term::ANSIMenu->new(
   width  => 40,
:
:
:
   prompt => 'prompt: ',
   item_fgcolor => "YELLOW",
   item_style => ["BOLD"],
   selection_bgcolor => "BLACK",
   selection_fgcolor => "RED",
);
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