The flesh here is using the Reaper Undead Flesh triad, I've also used Deathworld Forest/Ogryn Camo/Nurgling Green as a good base, but that does give a much stronger green tint to it than here.
That comes out more like this
I'd advise spending some time with Google images and looking at how real wounds and diseases look, it isn't pleasant, but it does help you fix in your head how things would look, and whether you then try to replicate them, or subvert them in order to make them look more supernatural, it won't do any harm. (Excepting maybe a few nights sleep - do not look up necrotising fasciitis unless you've got a strong constitution.)