What material in the square cab? That is a cool lookin' piece.
Of the options you have shown, I personally do not care for the white, but again, that is my personal taste; generally I would probably tend to try to pull the colors within the host material if I had the color option (like you did on the stone with the pink around it) but each cab is it's own entity so to me there is no right way, just whatever you try that finally speaks to you and says, "This is an awesome impression for this piece". I don't know what color choices you have to work with either, and as you said, this is a concept you are just now playing around with.
I like others ideas about trying other metal/wire combinations, that is a great idea too- even like a wire/cord combo twist around the groove would be fun to try out. Brass would be cool looking with some of these cabs and copper too. I don't know how patina would react with the nylon fabric because I have never tried that before- definitely test out a sample to see if it discolors the material before applying it to a piece that has already been glued in place.
If you decide you want to explore more color options or different material types at some point, here are a couple of cool sites to explore:
http://store.jewelsinfiber.com/thanks.htmlhttp://www.leathercordusa.com/index.html