Far too much work.

print hexdegrade("FF9944", 3);

sub hexdegrade {
  my $hex = shift;
  my $degrade = shift;

  my $temp = pack "H*", $hex;
  for (0..length($temp)-1) {
    for (vec($temp, $_, 8)) {
      $_ -= $degrade if $_ >= $degrade;
    }
  }
  return unpack "H*", $temp;
}
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-- Randal L. Schwartz, Perl hacker