Recipe from Warhammer Official for Diseased flesh on Death Guard Units like the Bloat Drone skin.

1. Base Coat model with whatever dark base coat you like. For me, it's Vallejo Black Airbrush Primer
2. Cover the skin with 2 thin layers of Rakarth Flesh
3. Glaze the skin with a 6:1 ratio of Contrast Medium : and Guilliman Flesh
4. Dry brush the skin with Ionrach Skin and then a lighter layer dry brush with Deepkin Flesh
5. Now create a mixture of about 8:1 mixture of Contrast Medium and Volupus Pink to add to the outside parts of the skin or where it touches armor
6. Finish up with doing a 1:1 mixture of Lahmian Medium and Carroburg Crimson to add on top of any boils or really tight skin on the edges/sides of the model