Are you doing animation? you should not need to leave it rendering overnight for single scenes. If you have a GPU based engine and even a mid tier GPU you should be able to get good results in anywhere between 30 mins to a couple of hours. If you have hundreds of items to do, then perhaps look at using an offsite cloud service. You can send them files and they can do the heavy lifting.
As for specific colours thats something you will need to do manually (to my knowledge) unless you can program it in SketchUp with ruby.