[Qwertystop]

E-paper (E-Ink is a brand name) works by magnetically moving small black or white particles (suspended in fluid) for each pixel whenever it needs to change. It's a bit like an etch-a-sketch, it's an analog system at the low level. At minimum, the movement takes time. Also, the current state of the pixel affects the charge that needs to be applied for a given target state - that means either taking more time to calculate, getting an afterimage, or doing that whole-screen black-white flicker to clear everything out. Probably all three due to precision limits.

[moron4hire]

I don't know a nice way to say this. Your reply has added nothing to my understanding.

[Qwertystop]

Yes, it's a fundamental limitation. Changing colors means moving tiny bits of magnetic dust, and the amount of charge needed is based on where they currently are. This takes more calculation than just running electricity through a light, which can be done regardless of whether or not you were running electricity through it a moment ago. This extra calculation will always take more time, unless the simpler tech reaches a fundamental physical limit like how fast power can be cycled without something melting.