It's too bad that Word and Acrobat don't have default print to white-on-black options. I haven't had the chance to try out white on black text (I won't use epub or lrf). If you've got a link to any inverted texts (even just a page or two--I don't have Calibre at the moment and don't plan to download it again), I could load an epub or something up just to see what the inversion looks like