my $newfgcolor = "\e[38;2;" . join(';', $r, $g, $b) . "m";
...
my $newbgcolor = "\e[48;2;" . join(';', $r, $g, $b) . "m";

##</code><code>##

my %matches = (
    qr/hello/ => 'FFFF00',
    qr/world/ => '00FF00',
...
);

...
foreach my $rex (keys %matches) {
    if($input =~ $rex) {
        my ($r, $g, $b) = hex2rgb($matches{$key});
        ...
        last;
    }
}