The current colour kindles and kobos don't use real eink colour. It's just a bw screen with lcd colour overlay (eink kaleido)

The real colour screens are used on the remarkable (eink gallery) and they are indeed slow for full page updates though remarkable seems to have done a lot of smarts for local updates while drawing.

Ah, sorry for confusion. I meant to ask about non-color version of Kobo.

And colour E-Ink devices also have horrible contrast.