Thanks for bringing this up. What you guys are noticing comes from the way E-Ink displays interpret different kinds of content.
We all know that e ink is wonderful for the eyes, but it works within certain limits. When a book or doc contains more than just plain text, the device has to strike a balance. Pure black-and-white rendering gives the strongest contrast for text, however it makes images, diagrams and shaded areas almost disappear. Using a range of grays helps those visual elements stay readable, although it can make the text appear a little lighter than expected.
Because every file is structured differently, the same book can look slightly different depending on its format. If you haven’t already, it may be worth trying an alternative version of the file. Sometimes another format is interpreted in a way that results in stronger contrast. I noticed this when I read a book in ePUB vs PDF format.
We’re already exploring options that would give readers more control over contrast in the future. Your feedback helps us understand what matters most, so thank you for taking the time to let us know.