Not sure what your input looks like, but just testing with your string above this seems to work for me:

use strict;

while (<STDIN>) {
        s/[\s\(\)]+//g;         # strip optional chars
        my @matches = m/(\d+)|([^\d]+)/g;
        print join ":", grep { defined $_ and $_ !~ m/^(r|rd|red)$/i }
+ @matches;
}
[download]

Which gives the following on various runs:

$ echo "12345 (Gray) 6789 (Red)" |  ./red.pl
12345:Gray:6789
$ echo "12345 (Gray) 6789 Red" |  ./red.pl
12345:Gray:6789
$ echo "12345Gray6789Red" |  ./red.pl
12345:Gray:6789
[download]

Update: Ikegami pointed out that I missed the requirement that spaces/parens were optional, so I changed this around slightly (no longer just a one liner). Now we can just get the numbers and words out seperately and print them in order skipping any words (like variations of red) that you need.