sub darken_hexrgb {
	my ($hexrgb, $darken) = @_;
	my @rgb = map hex, unpack "A2"x3, $hexrgb;

	my $max = (sort {$a <=> $b} @rgb)[-1];
	return "000000" if $max <= $darken;

	my $fact = ($max - $darken) / $max;
	return sprintf "%02X"x3, map { int($_ * $fact) } @rgb
}