my $text = "This is a test for the word blue more things blue and then some very large text with a lot of things blue and done";

my $words_to_go = 0;
my @keeper      = ();

while($text =~ /(\w+)/g) {
    if($1 eq "blue") {
        if(! $words_to_go) {
            print "$_ " for @keeper;
        }
        print "$1 ";
        $words_to_go = 5;
    } elsif($words_to_go) {
        $words_to_go--;
        print "$1 ";
    } else {
        push @keeper, $1;
        shift @keeper if @keeper > 5;
    }
}