If you're using acrylics (which I suggest since they are less toxic), any rust/dark reddish colored shade will work. Another lighter shade is Georgia Clay, which looks quite good as well. The actual color shade is purely a personal preference. Again, if you're into acrylics, then the Folk Art, Americana or, my choice, Delta Ceramcoat are fine. You can find them in Michael's, Jo-Anne's or other craft stores. These work well but may need a bit of thinning (with water). They are not hi-end like Windsor & Newton or Liquitex, but are far less expensive.
Jerrman