[alaithea]

My thoughts exactly. It would be hard to find many people who almost exclusively read white on black, though. I think the groups people break down into are likely the average people from "book-land", where all is black on white, and techies who use dark background terminals, but are fluent in both. In which case, it would make the most sense to test people who have extensive exposure to both (techies) for comprehension, etc.