This is not as easy task for me. I remember an abstraction from the MTL library which kind of does what you are looking for — duplicate geos and give different colors to each object in the chain.
The logic behind that is not straightforward, though. After experimenting for a while I ended up with the patch below, which applies different colors to an iterative gemchain according to an array of hue values. Obiouvsly this is only meant as a starting point, hope it helps.
http://www.pdpatchrepo.info/hurleur/iterationsWithColors.pd