ITS EASY IF YOU HAVE XENOFEX FILTERS. I WORK AT A GAME DEVELOPER AND I CONCEPT AND TEXTURE. I'VE DONE THIS A MILLION TIMES. WHAT YOU DO IS CREATE A BLANK LAYER. THEN RUN XENOFEX "LIGHTING" FILTER. ADJUST SETTING TO YOUR DESIRE AND MAKE SURE THE LIGHTING IS BLACK. WHEN RENDERED YOU GET BLACK ORGANIC LOOKING PATTERN. NOW ADD INNERBEVEL IN LAYER OPTIONS. AND THEN CHANGE VEIN(LIGHTING) HUE. ADD YOUR FLESH TEXTURE IN AND UNDER A NEW LAYER. I'M GUESSING YOU KNOW PHOTOSHOP ENOUGH TO MESS WITH ADITIONAL TWEAKS AND LAYERS.