It is not clear to me what you are trying to achieve, but one way to create a colon-separated string from all elements of an array is to use join.

#!/usr/bin/env perl
use warnings;
use strict;

my @list = (5..10);
print "list = @list\n";
foo(@list);
exit;

sub foo {
    my $media_list = join ':', @_;
    print "media_list = $media_list\n";
}
[download]

Produces the following output:

list = 5 6 7 8 9 10
media_list = 5:6:7:8:9:10
[download]

Additionally, the code you provided does not compile, and has other issues which can be resolved using the strictures (use strict; and use warnings;).