I have been watching this picture a Long time , i think the kindle paperwhite 4 screen quality is very good .
Today，about this question : Kindle paperwhite 4 （KPW4）screen quality not uniform? what should I do? I share a little experience.
In fact, i think you need clear the color attribute in the txt source files . use Calibre – E-book Management .
First, In your computer install calibre software , The method is simple , please visit How to Download and Install Latest Calibre on Windows 10
calibre software homepage :
second, Import the e-book into Calibre, select the book, right-click – convert the book – convert one by one.