When it came to painting the viking undead, I had a search around for a palette. I wanted something greenish, to contrast with the red tones of the clothing and shields. I used this image as a starting point.

The zombies were primed white and then I glazed with a grey and red, to give an undercolour of shade. The rest of the steps I have shown below. Each colour is thinned and matt medium added to add transluceny.

Step 1 : Glaze grey and chestnut

Step 2 : Glaze dead flesh 

Step 3 : Glaze camouflage green

Step 4 : Shade darker green, round eyes, mouth, lining

Step 5 : Purple line under eyes, in mouth, stippled on feet and some hands

Step 6 : Dark red for blood on gums, sores, hands

In the last picture I have also picked out the eyeballs and teeth with a very light grey (white is far too bright for eyes and teeth). Once the rags and weapons are painted I added more shading to feet and hands and splashed on some gore.