Reading a white text with a black background is much easier on my eyes. In Logos 3, you could accomplish this "accidentally" by dragging the mouse over the text. However, when you do this in version 4 the text stays black and the background is shifted to blue.
What would really be nice is a feature like the one on the iPod T/iPhone Kindle: you can choose to switch the color of the text to white and the background goes black (I don't have an actual Kindle, so I don't know if this feature is on the actual Kindle reader).
I realize it's not really a big deal, but if you guys at Logos are ever sitting around with nothing to do, perhaps you could work on a feature like this.