I'd start with painting a horse in a different way than gw team did it - imo it's just too white...
about the skin: We have to bear in minds that long dead flesh in the middle of desert can have color from dark brown (wood-like) thru greenish-greay to papytus white...
maybe You have any vision of effect You want to achieve?
for my part i will start the skin with several wash of graveyard earth for the base
the shading graveyard + scab red for the middle shadow and the extremity of the muscles graveyard + liche purple
highlight (with zenithal effect) down highlight graveyard+drop of camo+bleached bone, the high highlights with graveyard+drop of camo green+skull white