I think Pearl is the third generation of grayscale e-Ink screens to be used in production models. Pearl finally does e-Ink grayscale correctly. I assume that the same will be true for color e-Ink screens in that it will take until about the third generation before they are really good. As Bezos said, that could take years. That photo of the first generation e-Ink screen looked washed out, so they have a long ways to go as far as improving the quality.

If you ever enlarge a portion of text from a color screen, say this forum page, you will notice that the text is not grayscale. It is mostly grays, but there are a lot of color pixels mixed in as well. Too me this is distracting as sometimes a too vibrant pixel grabs my attention and makes reading a pain. I think if you want to read books then grayscale is the way to go.