Hmmmm, a sand and brown color would work well I suspect, for older towns and the countryside.
Gray sounds better for more built-up, modern towns, due to stonework, I suspect.
Then of course, there's the whole issue of what color the sand is, e.g. white with a gray underlay, tan colored sand, etc., etc.. Depends upon where your planning, I suspect.
I'd watch reruns of the Pirates of the Caribbean, and/or Black Sails, or look up images for that using Google, for a decent start.
Can't go wrong checking out what others have done too.
Personally, I'd plan on the more rural dirt/sand boards for that olde style settlement appeal.