E Ink's vice president of marketing, Sri Peruvemba, says that the company is also developing a color display using four subpixels: red, blue, green, and white. The E Ink displays sandwich a layer of microcapsules between layers of transparent electrodes. Back-and-white displays use microcapsules filled with white and black submicrometer flecks, which are positively and negatively charged. When a voltage is applied to the electrodes, the flecks move to opposite sides of the microcapsules, rendering words and images on a screen, where they remain static until another voltage is applied. To achieve color, engineers put a color filter on top of the existing display, but since this cuts out light, says Peruvemba, the display needs to reflect more light than those on the market now.

One major challenge for color E Ink paper, he says, is designing the electronics that control the voltage applied to the microcapsules, which require "very intricate designs, patterns that literally have to address every pixel separately," he says.

The next major problem that all e-paper company's face is ensuring that an e-book page can refresh fast enough to satisfy a consumer used to the speed of LCD. The new Fujitsu e-reader takes about a second to fully refresh its screen, which is about five inches by six and a half inches in size. Khan says that Kent is working closely with Fujitsu to reduce the page flip to less than a second, but this will require extra electronics that could increase power consumption or the cost of the device. Currently, Fujitsu's reader can operate for 40 continuous hours and is already far more expensive than other e-readers.

Peruvemba says that E Ink's forthcoming color technology refreshes at the same rate as its black-and-white technology--about a quarter of a second. In order to get even faster, he says, E Ink engineers need to work on the basic chemistry to modify the particles and the fluid within the microcapsules, as well as to develop electronics to apply the right type of voltages. The company hopes to have products based on a color display by the end of 2010.