A Maya tutorial that shows how to use a UV pass to create a Custom Color Render Pass in Maya and how to use that for compositing. This Maya tutorial comes to use from Zeth Willie in two parts.
Maya/Mental Ray: Custom Color Passes (2010) Part 1 – UV Pass from zeth willie on Vimeo.
Maya/Mental Ray: Custom Color Passes (2010) Part 2 – UV Pass from zeth willie on Vimeo.