Well what have you tried? I haven't used the foundation paints too much to know the shades. So with my slightly limited palette, here goes.
Either start out with knarloc green or ork hide green
Then catachan green
Then it looks like a high light of maybe bestial brown, catachan green and bleached bone.
Thats my best guess. Remember you don't need to paint it exactly like that, painting the models your own way makes them unique.
And actually i don't really like that color for nurgle, it looks more brown than green and it doesn't look sick/decrepit enough for nurgle. I personally like a paler greener flesh. Like how GW paints the Pestigor models or even a lighter shade of the green they use for Plague Bearers.
Well hope I helped. Also pictures would be nice.