I had to change:

  for my $i (@$grad) {
    push @rows, Tr(td({-bgcolor=>$i}, $i));
  }
[download]

to:

  for my $i (@$grad) {
       push @rows, Tr(td({-bgcolor=>"#$i"}, $i));
     }
[download]

and it works great. This is going to be fun to play with.. There seems to be a module for everything, but it's also cool to see it laid out like this..