Take a look at Spreadsheet::WriteExcel::Styler. It makes highlighting simple:

#!/usr/bin/perl

use strict;
use Spreadsheet::WriteExcel;
use Spreadsheet::WriteExcel::Styler;

my $workbook = Spreadsheet::WriteExcel->new('output.xls');
my $worksheet = $workbook->add_worksheet();

my $styler = Spreadsheet::WriteExcel::Styler->new($workbook);
$styler->add_styles(
   highlighted   => {bg_color => 'yellow'},
);

my $data = "OK";
$worksheet->write(0, 0, $data,
   $styler->({highlighted => 1}));
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