I agree with warh, you need a little bit of skin tone in there or they don’t look right. I like to give my castellans a nice redish hue as well for their burnt skin
All that was previously said aside (I just found this thread), my advice would be to look at the picture of the witchelves more closely. You don’t really get a lot of contrast, because all your colours start from black.
Why does the grey skin/black hair work with the witch elves? Because they started from a codex grey base… there’s no black to be found on the skin.
Start your flesh codex grey, and work it up with mixes of bleached bone. Then you’re skin gets a bit lighter, and you get more contrast with the black beards.
Also, your red and metallics look quite dark. My best advice there is also to start from a baselayer that isn’t black, or use something else than devlun mud washes or badab black washes.
Just my two cents. I do like the fact that you’re going for something else than the standard fleshy skin. Good luck on your quest!
My advice would be to start with a non-grey colour as a base, like others have suggested. I think you can use pretty much any colour. Blue, purple, and brown work. Red should be good too. Just make sure it’s not too bright. You can tone colours down by mixing with grey or a neutral colour.
I use a touch of real flesh tones when I’m painting blue or grey skin. Use it on extremities of muscles, lips, jaw etc. I find it stops the model looking too cold and brings it too life!