If you select an object in your sketchup model and then right click, at the bottom of the list you will find Vray Object ID which you can then use to assign values to various objects in you scene. Then if you have an object id render element you will see object rendered a color based on the value you assigned them. The colors are randomly assigned but everything you assign as 1 will be the same color. It takes some fiddling with and I find that material id usually does the job better but you never know when this would come in handy.