Color epaper screen tech is not having much commercial success, what with Mirasol abandoning the market and E-ink's color screens remaining expensive niche products, but that doesn't mean that the research has stopped.
Ricoh has just unveiled their latest prototype for a 3.5" color epaper screen that gets its color from 3 stacked layers of cyan, magenta, and yellow colored filters.
This new prototype builds on past research that Ricoh has been conducting for some years now. They showed off an earlier prototype at SID Display Week 2011, and from what I can tell they first announced commercial plans for the screen tech in 2009.
In the past 4 years they have incorporated a number of improvements, including a way around the need to wire and trigger each layer using a separate set of electrodes. The new prototype instead uses a TFT backplane to control the screen. This type of backplane is used in LCD, Pixel Qi, and E-ink screens, and both E-ink and Pixel Qi adopted it for the same reason as Ricoh; it lets them reduce production cost by using existing LCD factories with only slight modification.
The 3.5" prototype shown above is the same size and resolution as the original iPhone, but Ricoh is working on larger sizes.
It's said to be two and a half times brighter than current color filter displays and have a color reproduction range of 35%. That last doesn't actually tell us anything useful; the colors a screen can rpoduce are either experessed as a total number of shades (i.e., the Triton 2 color E-ink screen can show 4096 colors) or as a 2 dimensional graph (see gamut).
Ricoh had planned to get this on the market in 5 years, but this prototype makes me think they won't pull it off. It still takes too long to change the image. In the video the Ricoh engineer says that it takes over a second to refresh each of the 3 colors. That's simply unacceptable on a consumer product, IMO.