Like I said, I don't like my tanks clean, and I wanted this lot to look not-Imperium but not entirely clean Tau.
For this effect it's all about multiple layers over a fairly light base colour. On this I made shapes with blu-tak over a skeleton bone base colour then spray-canned light green, light grey, then light sand, successively removing strips of blu-tak. Then went round all the crevises with sepia wash fairly liberally and smearing it downwards a la gravity with a convenient finger. Next was highlights with a light sandy big fat drybrush. Then a few edge and corner chips with gunmetal/silver over dark brown followed by running a BB pencil around the edges of the tank to roughen it up more. The most wonderfully messy bit was using weathering powder and MIG pigment fixer which you can use to get either a smooth smeary graduation or get it to clump together as on the front of the dozer blade. Hours later after the fixer had dried I went round with a rough brush and finger smeared the bits I wanted softer. The dozer blade clumps will likely erode over time but I'll just re-apply if needed.