If we talking about replacing shadow with a colour rather than colour from transmitted light I've only seen this done at the material level (Blender tutorial on the Cycles render engine) - the light intensity from one render pass was applied to a blender node on a second pass. For this to work you would need to change every material  on every object that will receive the shadow so this is not a practical solution for anything other than simple scenes.I've attached a screen shot of how it can be sort of done in Poser but as you can see from the Blender settings its not a strong effect.