I have a small visual (optical) handicap and find it uncomfortable to read from devices that have a light background and dark text.
I am able to change to a black background with white text on my Kindle Fire HD8's Kindle app, as well as Kindle for PC on my desktops and laptops.
Try as I might, I have been unable to find settings for those properties in your KPW eLibrary Manager app. Have I missed them somewhere, or are they just not there? If they're NOT there, are they planned for the future?
Is there a PAID upgrade to your app? If so, what are the dirrerences between it and the free app?
BTW, I'm using Build 20160320.02.B [2.1.1/74/28] on my Kindle HD8.