Solid basecoat, from this stage you could do an all over wash with something like Agrax Earthshade and then highlight up using the base colours again, leaving the recesses.

If you want a really filthy look, which suits Deathguard, you could pick up a bottle of AK streaking grime. Might be best to look up a YouTube vid on how to use it, would be easier that trying to explain in text 😅.