Yes it is normal with eink devices. If you want to maximise the super-crispiness for every page you can go to
Settings - Reading settings and change the
'Refresh the screen every' setting from 6-pages to 1-page. Obviously you will see more frequent flashing, though. Or set it somewhere in the middle at 3-pages. I use 1-page myself. I learned to 'tune-out' the flashing years ago.
P.S Welcome to MobileRead and I hope you enjoy your new gadget
