I tried using the ColorMapping post effect and was very pleased with the results. No matter where I put my lights there was no blow-out, just beautiful soft fills. And it gave a nice sharp darkness to my shadows too.
But my Multi-Pass layers are tragically unaffected by it. They look the same as a render with no post effect applied (Color Mapping, does NOT show up in the Post Effect layer).
I'm guessing it's one of those things that only effects the beauty pass. Is that correct? Why use it at all?