Problem solved, but perhaps this little CGI script will be of service to you. It uses Color::Spectrum to generate a 12 cell, one row table whose cells range from the starting color to the ending color.

use strict;
use warnings;
use CGI;
use HTML::Template;
use Color::Spectrum qw(generate);

my $cgi  = CGI->new;
my $tmpl = HTML::Template->new( filehandle => \*DATA, associate => $cg
+i );
my $vars = $cgi->Vars;

if ($vars->{go}) {
    my @colors = map { c => $_ }, generate( 12, @{$vars}{qw(start end)
+} );
    $tmpl->param( colors => \@colors );
}

print $cgi->header, $tmpl->output;

__DATA__
<form method="post">
Color 1: <input type="text" name="start" value="#" /><br />
Color 2: <input type="text" name="end" value="#" /><br />
<input type="submit" name="go" />
</form>
<tmpl_if go>
<table width="100%">
<tr>
<tmpl_loop colors><td bgcolor="<tmpl_var c>"><tmpl_var c></td></tmpl_l
+oop>
</tr>
</table>
</tmpl_if>
[download]

You might be able to use this to generate your candidate ranges to see if they work or not.

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)