Basic white will usually get the best results. I realize that you are probably tempted to use a cheap paper because or the size of the mailing but remember a few new good customers should pay for the cost of the mailing. Including the better paper. What this means is that each letter can be personalized to the person it's addressed to. Instead of Dear Occupant or Dear Sir or Madam, it will say Dear Mr. Smith or Dear Mrs. Jones.
Response is usually higher when personalization is used.
If you are not able to do this for some reason try and be as specific as you can in generic personalization. Dear Gallatin County Voter for example. The reason being they have not captured your interest in what they are talking about. It's the same with your direct mail letter. The first paragraph must contain information they need or want that grabs their attention immediately or your information is destined for the wastebasket.