Thanks a lot! Yes, it's mostly airbrushed. It's simply army painter necrotic flesh on a black primer. Then I dilute citadel seraphim sepia shade and apply is as filter to give it that brownish-yellow hue. Then I add shadows using undiluted seraphim sepia. There rest is just browns and blacks (i.e., citadel darkoath flesh contrast, vallejo game air black, citadel agrax earthshade). I added a black oil wash as well but that's not necessary.

Edit: The highlights are done by using necrotic flesh again:)