The last few weekends I have been scenicing the area around my Fairy Hill Loop area. This involved putting polystyrene down, contouring it, and then throwing around a bit of plaster. As documented in this blog I went one further and also threw a fair bit of sand and dirt down and various shades of green scatter. If I don't say myself, I'm very happy with the results achieved. They will only get better as more detail is added.
So to answer a question posed to me, I will elaborate on how and what I did.
Normally I paint the ground a base colour and then sprinkle various tile grouts down to create the initial dirt layer so the white plaster does not shine through. However, friend of mine, Mike Boyde, gave me many packets of various colours of dirt and sand that he collected from the side of the road around the Toowoomba region a while back. So I thought I might give these a try. So I used the various black and brown soils then the creams and whites. Then over the top I used various types of scatters. The complete list is Testuff Scenimat Scenic Scatter, various Oz Flock colours - 101, 105 and 116. Some Heki Green Scatter and Woodland Scenics Fine Grasss T44. I prefer the really fine ground foam in preference to the hundred and thousand shape - elongated stuff. I also prefer the packets with all the same colour and not those that have a variety of colours in the same packet as they look very toy like. So to answer the question posed to me by Wayne Oliver, I start with the Yellow colour, and then mix the various shades of greens mid, light and dark. I just keep adding the various colours until it looks nice. Every now and again I spray over a mix of whiteglue and wet water from a spray bottle.
Side Note:- While in the shed yesterday with my two kids, I had to laugh as I had completed scattering the sand and soil around, I moved onto the yellow Oz Flock scatter on the other side of the tracks at Fairy Hill Loop when my 4-year old said to me, "That yellow is for dead grass isn't it Daddy?" It certainly was. Oh - the Joys of Model Railways!