Direct-mail designers follow trends with the color they use
They test one color against another with the same mailing, just to see if a purple carrier gets better response than a brown kraft. Fifty percent of the list gets a brown kraft and 50 percents get a purple carrier.
But you can use a test of your own. Watch your mailbox for the next 30 days for colored envelopes. If you see a certain color being mailed to you on a rather consistent basis, it probably means it’s working for the pros in direct-mail houses. It might be worth you trying yourself.
Postage is another way to give impact to the carrier
First Class is always preferable and will always get better returns. I’ve done mailings that have three commemorative stamps on the carrier and then four more on the reply envelope. It conveys a personal touch — like one letter being written to one friend, not 10,000 — and it always gets better response.