Everyone is going to have a different take on this so here is my two cents worth.
Then I dabbed a thin blotchy coat of yellow ink over the whole skin surface. The less uniform the better.
Using thinned down purple inks I painted in the recesses of the eyes, and the hollows of the cheeks.
With black ink straight out of the bottle, I painted on some of the larger veins on the side of the face.
Again using the straight black ink I paint a bit sloppy around the nose, mouth, and visible wounds (zombie blood is rotten too so I use black).
The other two examples are zeds I painted at the same time.
The yellow and purple inks are GW and not longer in production.
The gray is Reaper and again is out of production.
The black ink was purchased from an art supply shop. Just look for India Ink.
My two cents. I hope you like.