Here's a picture of a work in progress Skaven Stormvermin. I'm trying to paint it rather quickly and trying a few different techniques. All the metallic areas were painted with Chainmail and given a heavy wash of Badab Black followed by a very thin wash of Vermin Brown. I find that the Vermin Brown wash adds some subtle rust coloration to the armor areas. The pictures don't show the depth of the armor colors.
I've decided to paint my Skaven army as real rag-tag colors so they'll have all manner of cloth colors wherever they've managed to scavenge it from.