Since almost all hashes and arrays I make end up getting passed to subroutines, I usually just create them as refs. This has the (slight) benefit having a consistent point of dereference in mainline code and subroutine code instead of having to remember to move the arrow around. Also foo($this) looks nicer that foo(\%that).

RefFoo

#!/usr/bin/perl

  use strict;

  my %rgbs = (
    yellow  => { r => 0xff, b => 0,    g => 0xff, },
    magenta => { r => 0xff, b => 0xff, g => 0,    },
  );

  print "$rgbs{yellow}->{r}\n";

  foo(\%rgbs);

sub foo {

  my $rgbs = shift;
  print "$rgbs->{yellow}{r}\n";
}
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