use strict;
use warnings;

my $string = '111111111:22222\:2222:333333333:4444444';

my @split  = split(/(?<!\\):/, $string);

print "Results:\n";
map { print "$_\n" } @split;

##</code><code>##

Results:
111111111
22222\:2222
333333333
4444444

##</code><code>##

my $string = 'AAA:BBB:CCC\\:CCC:DDD";