#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11146126
use warnings;

# Given path: /a/b/c/d
# Given regex: ^/a/b/([^/]*)/([^\/]*)
# Output: /a/b/\033[1;31mc\033[0m/\033[1;31md\033[0m

my ($boldred, $reset) = ( "\e[1;31m", "\e[0m" );

my $string = '/a/b/c/d/';
my $regex = qr{^/a/b/([^/]*)/([^\/]*)/};

$string =~ $regex or die "no match of $string by $regex";
my $coloredstring = $string;

my $count = @- - 1;
for ( reverse 1 .. $count )
  {
  substr $coloredstring, $+[$_], 0, $reset;
  substr $coloredstring, $-[$_], 0, $boldred;
  }

print "$coloredstring\n";
use Data::Dump 'dd'; dd 'coloredstring', $coloredstring;
[download]

Outputs:

/a/b/c/d/
("coloredstring", "/a/b/\e[1;31mc\e[0m/\e[1;31md\e[0m/")
[download]