my $red = undef;
my $green = undef;
my $blue = undef;

sub change{
  my($color1, $value1, $color2, $value2, $color3, $value3) = @_;
  ${$color1} = $value1;
  ${$color2} = $value2; # maybe: if defined $value2;
  ${$color3} = $value3;
}

change(\$red, 42, \$green, 255, \$blue, 11);

print "($blue)";

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;

my %COLORS = (
  red => undef,
  green => undef,
  blue => undef,
);

sub change2{
  my($R) = @_;
  my %H = %$R;
  for my $key (keys %H){
    $COLORS{$key} = $H{$key};
  }
}

change2( {red=>5, green=>6, blue=>7} );
print $COLORS{red};