Thanks Samuel!
OK,here is how I painted them. Just note that this is NOT what I invented.
All I did was following an article on Armour Modeling Vol.54 April issue 2004.
First,paint the whole track surface with gray. I used my original gray which is 90% gunmetal(Mr.color No.28), 10% light gull gray(No.11) and a very small amount of flat bese.
A guy I know uses simple flat black as base color but I found it little too dark.
Second,ready some powdered pastels.Weathering pastel sets from Mr hobby are easy and fine.
Mix them as you like to make 2 or 3 different tone of brown. Drak brown,sand,light sand, stuf like that. Anyway you want but just don't use them straight out of the jar.
Then add some TAMIYA acrylic thinner(X-20A) to one those browns and make a mud paste.
Aplly the paste to tracks,wheels and the hull with a brush and add dry different color patel powders which you make on wet surface using another brush.
There is no rules or specific patterns. It is dirt.
Do not rush to finish it all at one time.
Practice first on the bottom surface of the hull and see how it goes.
Third,when all the pastel powders are dry, use cotton swabs and a hard brush to scrab off some pastels so that you can see some surface of tracks or the edge of wheels.
Finally,dry brush tracks with silver (TAMIYA enamel color).
I am sorry for my poor choice of words.
I hope this helps
