The Hlist widget needs to use Tk::ItemStyle instead of tags. It is one of the problems with Tk, that the interface is not totally standard across widgets. Try this:

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
use Tk::HList;
use Tk::ItemStyle;

my $mw = MainWindow->new();

my $green = $mw->ItemStyle(
    'text',
    -stylename => 'green',
    -bg        => 'green',
    -fg        => 'black',
);


$mw->optionAdd("*background", 'red');
$mw->optionAdd("*foreground", 'blue');

my $hlist;

$hlist = $mw->HList(
    -itemtype   => 'text',
    -selectmode => 'single',
)->pack(-fill=>'both',-expand=>1);

$hlist->columnWidth(0, -char, 90);
                    
for (1..1000) {
    $hlist->add($_, 
    -text=>$_);
 }


for (my $i = 1 ; $i < 1000  ; $i += 2){
    $hlist->entryconfigure( $i, -style => 'green' );
}

MainLoop;
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