The major difference between your average e-reader and a tablet is that tablets use a backlit liquid crystal display, while e-readers display their content using something called e-ink. What is e-ink exactly?
How does it work?
When you look at an e-ink screen, it looks like it’s covered with a flat pane of glass — but in fact, an e-ink display contains millions of tiny cells that are so small, you can’t really see them with the naked eye. Each one of these cells is full of positively charged capsules filled with white pigment, negatively charged capsules filled with black pigment, and a clear ink or oil for them to float around in.
The application of a positive or negative charge to the capsules causes either color of pigment to float to the surface. Applying a different charge to each cell in the display results in a different color for that cell. The end result, on a macro level, is the configuration of words and pictures you see on the screen.
Why does e-ink work so well in the sunlight?
Behind the cells on an e-ink display, there’s a reflective surface that reflects environmental light rather than creating its own like an LCD does. While an e-ink screen reflects ambient light back at your eyes (like a piece of paper would), an LCD display reflects light everywhere off its surface — and the light it produces is harder to see when it’s bright out, for the same reason it’s easier to see a well-lit room through a window at night than it is during the day.
Is there color e-ink?
While color e-ink does exist, it’s not available in any popular e-readers on the market today due to the cost of producing a device that supports it and the fact that the colors tend to look washed out. Maybe someday, though.