my %ch = ('green' => 'lousy', 
          'blue'  => 'cool', 
          'pink'  => 'mini' ) ;
my $str = 'I have a green hat, blue shirt, plus a pink jacket';
print $str . "\n" ;
$str =~ s/(green|blue|pink)/$ch{$1}/g ;
print $str ;


__END__

I have a green hat, blue shirt, plus a pink jacket
I have a lousy hat, cool shirt, plus a mini jacket