Recently vendors have been releasing e-readers with colour E-Ink screens (the Onyx Boox Poke 2 Colour and Pocketbook Colour are two examples). We also witnessed the release of a colour E-Ink smartphone by HiSense. The latest e-readers by Onyx and Pocketbook are using E-Ink's Kaleido colour technology (Triton was the previous generation).
The question is if Kaleido is genuinely useful for reading. I would answer in the affirmative for a niche userbase - these are users that need colour for reading, for example, specific textbooks, graphic novels and manuals. Beyond reading and note-taking, then the limitations of E-Ink apply as Kaleido is based on Carta but with the addition of a colour filter. Thus, while Kaleido is a useful feature for an e-reader, the limitations of E-Ink render it useless for smartphones and multimedia.
At the moment, the potential e-paper candidate for multimedia is CLEARink. In 2019 CLEARink announced it is collaborating with FLEx Lighting to produce a video-capable display. However, it is not clear when the technology will be widely available.