I fretted about for a long time on how to paint possessed Chaos Space Marine flesh. I want it to be some combination of what I would have done for normal human skin and what I would have done for daemon skin. Here's what I got out of it.
Step 1: Rakarth Flesh
Step 2: Praxeti White
As a drybrush step, I picked the "dry" white paint. We only want edges and raised areas picked out here. Also, there will be a lot of washes, so don't worry if this comes out a little messy.
Step 3: Reikland Fleshshade
This is the final step for what I would do if it were just normal human skin. The idea here is to move forward and elaborate more to make it inhuman.
Step 4: Druchii Violet
I love purple, and want this to end up being my unaligned daemon skin-tone. I'm purposefully keeping the wash away from extremities here, notice the fingertips. This is where I would normally stop for a Slaaneshi daemon's skin... and then elaborate with more pinks across the model... so we're going to keep going.
There's some interesting stuff going on with the Possessed models, in that there are areas where it looks like the armour has fused with the daemon, and I want to play off of that a bit. So our last step will be to bring the skin closer to the armour.
Step 5: Nuln Oil
Note that the model itself is not "done" yet, as even in the face (which is incredibly dark, I know), I have yet to pick out the eyes and teeth in that last pic. Here's what that looks like:
What do you guys think? The effect works really well in my opinion due to the black armour... Not sure how it would look with other legions, though.