This is how E Ink technology in reading displays work, and how they differ from other screen displays.
E Ink was founded by a company that shares the same name as their product "E Ink", and its technology has been around for much longer than you might think.
Remember those sketch board toys you probably played with as a kid? E Ink, at a fundamental level, works exactly the same way.
E Ink displays offer a screen that is usually monochromatic in appearance and is designed to put no strain on the user's eyes in e-reader tablets. E Ink displays work by using the same ink as you get in a pen, but rather than using paper as your canvas, E Ink makes use of tiny capsules that have a diameter of around the size of a single human hair. And, like the toy sketch boards, E Ink is sensitive to magnetic fields. The black and white ink pigments are differentiated with the use of either a positive or negative charge and are kept separate by the use of a specialized liquid.
When the e-reader flips to a new page, it simply arranges the positive and negative charges in relation to the text that needs to be displayed and the ink forms perfectly over those areas, thus giving you a page to read.
Take a look at the video below by Gizmodo on YouTube, titled How E Ink Works.