LCD screens don't need contrast or saturation adjustment unless you are a design or photo professional. For any screen really, you set the contrast at the proper level if it isn't already there from factory. We adjust brightness because the brightness of our environment changes during the day.
As I read the thread, the discussion is about reading text on a laptop or mobile screen. For that you need nothing else than brightness controls. And 100% black text on 100% white background is a good default and works well for all users.
