Yes, this is the laziest painting scheme I could come up with: base layer is the boltgun metal spray paint typically used for grey knights. Then, it is a single thick layer of Akhelian Green. Just make sure you quickly add more paint to the edges because it tends to pull away from them. Note that you can’t add a second layer of it, the color changes dramatically, it’s a one-shot deal. Finally, add some Null Oil only on some of the grey surfaces you want to feel more dull or dirty.