I use three colours to paint some wood. Paints aren't from GW but colours are almost like same. Chaos Black, Scorched Brown and Graveyard Earth. First paint balsa to black and after that 1:1 mix of black and brown. When paint is dry I tone it up by adding more brown using dry-brush technique. And last layer is 1:1 mix of brown and GE also by dry-brushing.