Cloth usually has more texture than armor, so do a light drybrush of your highlight color all over, even if that isn't your normal technique. Don't use any gloss, since I think that will take away from the robes feel. Cloth also picks up lots more dirt and stains, so bring the colors on your base into the bottom part that would drag or get dusty. Cloth also absorbs, so there's no blood spatter, just darker soaked in blood stains.