$class = '...';
$color = color_of($class);

sub color_of {
    $class = shift;
    my $t = first { $class =~ /$_->{'re'}/ } @rules;
    return $color->{'color'};
}

##</code><code>##

for my $foo (...) {
    my $color = first { $class =~ /$_->{'re'}/ } @rules;
    $color = $color->{'color'};

    ...
}

##</code><code>##

my $color = ${first { $class =~ /$_->{'re'}/ } @rules}->{'color'};