If you want to just split on the 1st :, use split with a LIMIT of 2:

use strict;
use warnings;

my $s = '          Aggregate:    f3050-184-160:EmptyAggr';
my ($first, $rest) = split /:/, $s, 2;
print "$first\n";
print "$rest\n";

__END__
          Aggregate
    f3050-184-160:EmptyAggr
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