Personally, I'm not interested in the whitest whites and blackest blacks. Most books don't have the whitest paper, I don't choose the highest brightness factor when I buy printer paper, and whenever possible I set background and foreground colors on my computer and tablet applications to be less stark than pure black/white (see
Solarized for a well designed palette that's easy on the eyes).
I find the Aura HD has a very comfortable contrast to my eyes. In fact, if anything, I'd prefer to have a contrast adjustment to tone down the whiteness of the background a bit when using the frontlight.