I'm planning to build an OIF vignette w/ Dragon's Modern US Marines. The three soldiers(I didn't include the MGunner) will be behind 2 intersecting walls. What color will be appropriate for the wall? would it be concrete color or sand color. The walls will be tattered w/ chip-offs to look really old. Thanks

To be honest, it can be whatever you like. If you look at some of the pictures from Iraq and Afganistan, the buildings in the cities are usually a cement skeleton with brick infill. In small towns and vilages, they seem to have used adobe style building, so you would have very tumble-down walls of consistent yellow/sand colour.