Two quick cellphone shots to illustrate some of the settings.
Backlight is set to night and 8, which is good setting for reading books I find, contrast for both the comixology as well as the Perfect Viewer apps was actually optimized for night an backlight set at 16, so you can get even more contrast out of this thing.

(Also, darker details might become more visible, kerning then doesnt seem that pronounced).
Smartphone white balance took away some of the orangey glow.
Comixology (longpress the app icon, set "start custom greyscale adjustment: Text: 0, Picture: 29")

src: From Hell
Perfect Viewer (Saturation: 100, Lightness: 17 (or 25, depends))

src: 20th Century Boys
For perfect viewer set the image to be centered, and half pages only - this will split double pages and prevent you having to press two times for every page turn. You can still scroll a page up and down, if something gets croped in the default position, but with mangas thats actually hardly ever needed. Also, with these settings I also have screen transitions left>right enabled. It softens the image and makes it more readable..

(could have also gone the other way round, and maybe not used a saturation setting as high...

)
Also set exit as a one touch action for upper mid (or any other position on the touchscreen), so exiting the app becomes quicker.