How Do I Adjust the Background Color in the App Reader?

To change the background color or the Reader, do the following:
Tap the icon in the upper right hand corner of the screen.

Tap "A" in the banner of the sub window.

There are 3 options for background color: White, Black, and Sepia

Select the color option you desire. It will be reflected in the Preview Window. Press "Close" to dismiss the window

The changes are applied to the eBook