Ok, there are a few ways to do it.
I play VC in fantasy and my ghouls have a very similar skin tone to that nurgle general. What I did is the following:
Basecoat with a mix of Tanned Flesh and Codex grey
Highlight through adding progressive amounts of elf flesh (and some Codex Grey when the mix becomes tooo lively)
Wash with Devlan Mud
Redefine the Skin with a thin layer of your last highlighting colour
Add final highlights with Elf Flesh + Bleached Bone
If you think it is too dark give it a slight wash with Griphonne Sepia afterwards and you should be fine.
Thats about what I did off the top of my head. Here is what it looks like:
Hope this helps