What Does This Error Mean?

Nook Night Mode inverts the screen colors to white text on a black background — it is found in the reading settings menu (Aa icon) inside a book. If Night Mode is toggled on but the screen does not change, restart the Nook and open a different book to test.

Affected Models

Nook GlowLight 4
Nook GlowLight 4e
Nook GlowLight Plus 7.8
Nook Tablet 10.1
All Nook e-reader models

Common Causes

Night Mode applied inside a book that does not support custom themes — some sideloaded formats override display settings
Night Mode toggle found in reading options not being saved between sessions on some firmware versions
Nook backlight at maximum brightness making Night Mode hard to notice — reduce brightness too
App cache conflict preventing display settings from applying
Night Mode not available in PDF viewer — only works in the Nook reading app for EPUB files

How to Fix It

Enable Night Mode from inside a book.

Open any EPUB book and tap the center of the screen to show the reading controls. Tap the Aa (text settings) icon and look for a Day/Night or Theme option. Select Night or Dark theme — the change applies immediately to the current book.
Also reduce the frontlight brightness.

Night Mode works best when you also lower the frontlight brightness. Swipe down from the top of the screen or tap the brightness icon in reading controls. A white background at full brightness with Night Mode enabled may still appear bright — lower brightness to 20–40% for a comfortable dark reading experience.
Check if the book format supports Night Mode.

Nook Night Mode works in the standard EPUB reader but may not apply to PDF files, Nook Kids books, or certain publisher-locked titles. If Night Mode does not work on one specific book, try it with a different book to confirm the feature works. PDF files have their own viewer and do not support Nook display themes.
Restart the Nook.

Hold the power button for 3 seconds and select Restart or Power Off, then turn it back on. A restart clears the display cache and often resolves Night Mode not applying correctly. After restarting, open a book and re-enable Night Mode from the Aa settings.
Clear the Nook reading app data.

Go to Nook Settings → Apps → Nook → Storage → Clear Cache. This resets cached display preferences without removing your library. After clearing, open a book and set Night Mode again — it should apply and persist correctly.

When to Call a Professional

Night Mode is a display preference built into the Nook reading app. If it consistently fails to apply after restarting and reinstalling the app, contact Barnes & Noble Nook support.