I was asked how i painted these models recently so thought i would post it here.
Basically the carapace is built up layers of lines, over a black undercoat. It starts very dark brown[scorched] then goes through mid browns, to snakbite leather which i then added white to to get to the desired colour. When doing the lines you make sure each layer goes over the last, leaving a little of the previous layer underneath. Also make sure the lines are not too uniform, varying teh length every now and then to give a more natural look