Well this is one of those not so helpful replies, but...
Please, please, don\'t do the green tinted skin choice! I\'ve seen a million Nurgle Marauders with the pale green \"sick\" look and I hate it. It just doesn\'t look good at all IMHO, no matter the skill involved....
Personally I think you\'ve got the brush skills to do anything you want, but I would go for a good variety of greyish and purplish skin tones. DragonsReach mentioned in another thread that using grey in skin tones creates a really aged feel to the skin which I feel might look a little better than the standard green look.
So there\'s no help from me, only a request and an opinion from the peanut gallery.