Comics, graphic novels, manhwa. Colour illustrations in books. The presence of colour can enhance the reading experience. While still retaining the qualities that make eink/epaper better for reading.
I'm sure there are more uses for it, but our inability to come up with those uses does not invalidate its potential
Plots in research papers (although I guess they should be understandable in grayscale if for no other reason than accessibility, unfortunately that is sometimes skipped...).
I'm sure there are more uses for it, but our inability to come up with those uses does not invalidate its potential