use strict;
use warnings;
use Tk;
use Tk(qw/NORMAL_BG/);
use feature 'say';

my $mw = Tk::MainWindow->new;
my $bt = $mw->Button(-bg => 'green', -text => 'green')->pack(-fill => 'x');
say 'background ', $bt->cget(-bg);
my $col = NORMAL_BG;
say "default background $col";
$mw->Button(-bg => $col, -text => $col)->pack(-fill => 'x');
$mw->Button(-text => 'default')->pack(-fill => 'x');
MainLoop;