How about this attempt - do not hardcode your regular expression, use a 'split' on record boundary instead.

#!/usr/local/bin/perl -w
use strict;

chomp(my @lines = <DATA>);

my @array;
foreach (@lines) {
  foreach (split /(?<!\w)(?=\w+::\w+::\w+)/) { # <- split on record bo
+undary
    s/\|$//;   # get rid of the last | on the line
    push @array, $_;
  }
}

print "$_\n" for @array;


__DATA__
monsa::clear::1|red::23|blue::50|monsb::clear::80|red::90|blue::100|
monsc::clear::1|red::23|blue::50|green::50|monsd::clear::80|red::90|
[download]

And the output is -

monsa::clear::1|red::23|blue::50
monsb::clear::80|red::90|blue::100
monsc::clear::1|red::23|blue::50|green::50
monsd::clear::80|red::90
[download]