Color eInk isn't being done because it's a technical problem, not a design problem. Everybody knows color eInk would be cool, we don't need Apple to step forward and say "You know what, color eInk would be cool!"
We just need somebody to invent a feasible one, make it and sell it. You'll then see it in Kindles quickly enough.
Color eInk isn't being done because nobody is willing to bet the farm on it. Everybody knows color eInk would be cool, and we DO need someone like Apple to step forward and say "You know what, color eInk would be cool! And here's a billion dollars, make it happen!"
We just need somebody to invent a feasible one, make it and sell it. You'll then see it in Kindles quickly enough.