I wanted to touch them up a bit for two reasons: all the ground was painted the same rust color as the wreckage and I wanted them to match my basing scheme.
I started by adding some modeling paste to a couple of bare areas, then added some small ballast on top of it. I also added a few pieces of medium ballast for larger pieces of rubble. I painted the ground areas with Vallejo Flat Earth. I then drybrushed a mix of Flat Earth and White. I painted the areas I wanted to be rubble with Ceramcoat Charcoal Grey, then drybrushed Ceramcoat Hippo Grey and Vallejo Stonewall Grey in succession. I glued on patches of static grass and a few tufts, then sealed it with 2 coats of matte spray.
Before and after pictures; click to enlarge.
Thanks for looking!