You can now assign different component shading groups for each of your render layers. Assume, for example that you have a plane on both layer one and layer two. In layer one, you can now assign half of its faces to a white shader and half of its faces to a black shader. Then, in layer two, you can assign half of its faces to a green shader and half of its faces to a red shader.


To assign different component shading for each render layer
 the
            object and select Face to convert to Face mode.
  the
            object and select Face to convert to Face mode.
          and
            select Assign New Material or Assign
               Existing Material to assign a shading group for the selected
            components.
  and
            select Assign New Material or Assign
               Existing Material to assign a shading group for the selected
            components. 
          the
            object and select Face to convert to Face mode.
  the
            object and select Face to convert to Face mode. 
            In this layer, you can assign component shading groups that are different from the first layer.