Originally Posted by ronw
It is quite annoying and tends to be disruptive to my reading
It's perfectly normal for eInk screens, and you'll get used to it very quickly. It takes ~1 second which is about the same as it would take to turn the page of a paperback book.
The reversed black/white during the refresh actually acts as a nice visual reminder that the page is turning. If the transition was immediate and seamless I think it would actually be hard to tell if the page had turned or not!
I find myself anticipating the end of the page, and hitting the right d-pad button while I'm reading the last line so that the refreshes just as I finish the page!