Couple quibbles:

1. re "not often used" is actually fairly common; it's been cited in at least two nodes in the past couple days
2. and re print RED,... my 5.10.1 under *n*x pukes on this (sees "RED" as a filehandle, illegally followed by a comma). Since ikegami has already referred OP to the docs on ANSI, please take this merely as an explanation of why I've used square-brackets rather than colorizing (we won't mention "lazy" here).

But a more substantive issue (perhaps) lurks in your split where your version will match "hit," "Hitachi," and many others including the vulgar word below (at Note 1):

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

# 840126

my @line = ('Not here: line 1',
            'This line 2 has a hit here and a hit there.',
            'hit me, hit me, bust me in line 3!',
            "Don't throw a shitfit over that hit in line 4.",  # *Note
+ 1 
            'Line 5: my search-word does not exist here.');

my $word = 'hit';
my $total_count = 0;

for my $line(@line) {
    my $count = 0;
    my $n = 0;
    my @stuff = split m/(\b$word\b)/, $line;
#   grep { $n++; if ($n % 2) { print $_; } else { print RED, $_, RESET
+; $count++; } }
    grep { $n++; if ($n % 2) { print $_; } else { print "\t[ $_ ]"; $c
+ount++; } } @stuff;
    print "\nFound $count times in the preceding line.\n";
    $total_count += $count;
}
print "Total count: $total_count\n";


=head execution:

ww@GIG:~/pl_test$ perl 840126.pl
Not here: line 1
Found 0 times in the preceding line.
This line 2 has a     [ hit ] here and a     [ hit ] there.
Found 2 times in the preceding line.
    [ hit ] me,     [ hit ] me, bust me in line 3!
Found 2 times in the preceding line.
Don't throw a shitfit over that     [ hit ] in line 4.
Found 1 times in the preceding line.
Line 5: my search-word does not exist here.
Found 0 times in the preceding line.
Total count: 5
ww@GIG:~/pl_test$

=cut
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IOW, I may have overwritten this, but using the word boundary metacharacter to restrict your matches (as in my line 19) is often a good idea.