• In monochrome panels, you can get 16 shades, and a full refresh in under a second (with partial refresh much faster, as tight as very few milliseconds for small areas, or commonly 30fps full-screen update if you’re willing to compromise a bit on image quality).
• In colour panels, you don’t seem to get shades or rapid refresh: seven colours means you get a seven colour palette, so you’ll have to use dithering to get any in-between colours; and you don’t get partial updates at all: even the fastest coloured panels take a couple of seconds to update the image, and the more colours you add the slower it is.
If I’m wrong about these and there are colour panels with more interesting colour or partial refresh, I’m interested to hear. I just haven’t seen any, and have done some looking.
The long and the short of it is that colour e-ink displays are only useful for display use, not for individual devices like ebook readers or computer displays.