I painted the inside of the draugr's mouth yesterday. It's much easier to paint the inside of the mouth before assembling it. Whenever I've done zombie skin in the past, I've used a mixture of burnt umber, burnt sienna, and altramarine paints. This process has always served me well, and I'm sticking with it now. I painted the teeth off-white, then went back over them with a brown wash.
Here's a photo looking down the draugr's gullet:
Here's the tongue in close up:
Draugr legends often describe the draugr as being a deathly blue colour - presumably blue-black as a result of decomposition. The body is reanimated, but it still decays and will eventually fall apart. I've made sure my paint colours are nice and dark with plenty of blue tones, but I may add some more blue-black streaks in the future. This should give the paint job some depth and character. Right now I've just painted the bits I won't be able to reach once the mouth is assembled.