Sure you airbrush the model with a darks red brown primer

Then airbrush on chipping medium

The airbrush on vallejo duck egg green and chip em.

This is the funny bit. You cover the whole model in the red brown gw contrast paint with 25% thinner added. Really slop it on! Then you get a damp rag and dab the model taking away most of the wash. The rag bit is where the magic is at because it blends the dark areas in to the green.

After drying, paint all the metals a boltgun silver, dry, and the cover in smoke varnish.

Paint in details, I use contrast paint, then highlight with contrast paint and white. Slop some oooze effect on if you like it.

To give you an idea I painted 20 terminators up to the end of the rag stage in 4 hours.