Gradient

sub {{ my $ret = [ map {int} @$c ]; ... ##

##

  $w = [ map {
       my $v = $f + $s*$_/$i;
       $f = $v - int($v);
       $v # not int $v
     } @$w ];
     $w->[-1] += $f;

##

##

use constant PI => 4 * atan2(1,1);

my $intervals = 40;
my $iterlin = range( [  0,255,255] => [  0,255,  0],
    [(1) x $intervals],
    $intervals );
my $itersin = range( [  0,255,255] => [  0,255,  0],
    [ map {sin(($_/$intervals)*PI) } 0..$intervals],
    $intervals );

print qq{Gradient
\n};

while (my ($rgb_lin, $width) = $iterlin->()) {
    my ($rgb_sin, $widthsin) = $itersin->();

    my $lin = join '', '#',
        map { sprintf '%02x',$_ } @$rgb_lin;
    my $sin = join '', '#',
        map { sprintf '%02x',$_ } @$rgb_sin;

    print qq{};
}
print "
$$rgb_lin[0]
$$rgb_lin[1]
$$rgb_lin[2]
$$rgb_sin[0]
$$rgb_sin[1]
$$rgb_sin[2]
\n";