my $twig = XML::Twig->new(
    twig_handlers => {
        keep_atts_order => 1,
        color           => \&content_handler,
    },
    pretty_print  => 'indented',
);
[download]

should be

my $twig = XML::Twig->new(
    twig_handlers   => {
        color => \&content_handler,
    },
    keep_atts_order => 1,
    pretty_print    => 'indented',
);
[download]

You should have seen that problem if you had indented properly. Boo for bad indenting!

Furthermore, by placing the atts in a hash before passing them to set_atts, you change their order before the module even sees them. Turns out set_atts accepts a list of key=>val pairs as an alternative to a hash ref, so change

$color->set_atts({...});
[download]

to

$color->set_atts(...);
[download]

I hope this is just for æsthetics. You shouldn't expect attributes to be in a particular order.