Some background: 
%var       - Hash
$var{$key} - Hash element
$var       - Scalar. No relation to %var

[download]

Excerpt from your code: 

return &Y::module_subroutine($hash_to_send);

sub module_subroutine {
   my($hash) = @_;
   return "The colour of the sky is ".
          $hash{third_colour};
}

[download]

Fix 1: 

return &Y::module_subroutine(%hash_to_send);  <--- Use the right var

sub module_subroutine {
   my(%hash) = @_;                            <--- Use the right type
   return "The colour of the sky is ".
          $hash{third_colour};
}

[download]

The above copies the entire hash (%hash = %hash_to_send;). To avoid that cost, a reference is usually passed. Fix 2: 

return &Y::module_subroutine(\%hash_to_send);  <--- Pass reference

sub module_subroutine {
   my($hash) = @_;                             <--- A ref to a hash
   return "The colour of the sky is ".
          $hash->{third_colour};               <--- Must dereference
}

[download]

In reply to Re: Transferring local hashes to module subroutines by ikegami
in thread Transferring local hashes to module subroutines by cowgirl

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