Using Schwartzian Transform here is overkill, because hash lookups are very efficient. Simplification:

my @letters = qw(
   red red red blue white yellow blue navy navy green white cars );

my %count;
$count{$_}++
   foreach @letters;

print("$_ => $count{$_}\n")
   foreach sort { $count{$b} <=> $count{$a} } keys %count;
[download]

Output:

red => 3
blue => 2
white => 2
navy => 2
cars => 1
green => 1
yellow => 1
[download]

Kudos for being the first to sort the results, though.