Enable Night-Reading Mode in iOS Apps - Easy Guide

Activate System-Wide Night Mode on Your iOS Device
For users who appreciate the new Night theme introduced in iBooks 1.5, a system-wide night mode for iOS is achievable with a simple adjustment. This allows for a more comfortable viewing experience, particularly in low-light conditions.
How to Enable the Night Mode
Digital Inspiration has detailed a resourceful method to replicate the dimmed and inverted-color Night setting from iBooks across your entire iOS interface. The process is straightforward and requires only a few taps.
To begin, navigate to the Settings app on your iOS device. Then, select General, followed by Accessibility.
Within the Accessibility menu, locate and tap Triple-click Home. Set this function to Toggle White on Black.
Using the Night Mode
Once configured, exit the Settings app and launch any application. A rapid triple-click of the Home button will activate the white-on-black effect, mirroring the iBooks Night mode.
To revert to the standard display, simply triple-click the Home button again. This toggles the setting on and off, providing convenient control.
Considerations
It's important to note a potential drawback. Images, both within applications and when browsing the web, will appear as color negatives rather than their original form.
Further details on this technique can be found at: Enable the Night-Reading Mode Inside Any iOS App [Digital Inspiration]