Hi
The thatch was over a black undercoat and is a dark umber (vallejo I think) dry brushed a couple of coats.
then some flesh tone added to the dark umber to just catch the edges in an upward dry brush, from bottom to top and along the ridge.
Hope that helps, I used a house near me as my reference, which has aged thatching. I must admit that so many folk seem to go for a thatch finish which seems to be the day after the roof has been put on!!
Simon.