Another feature I liked in another application is the ability to make previous paragraphs grey with the current text being black. There is also an option to make all but the current sentence grey. It purpose is to remove the temptation to go back and edit what you have written or just being distracted by it. In the case of the multiple text and background color choices in Scrivener, the goal would be to make the previously entered paragraphs or sentences fade somewhat into the background. One should still be able to read them with a little effort. This application also had keyboard shortcuts to turn this on and off. Again, my apologies if I missed this in the options.
Curt