https://en.wikipedia.org/wiki/Pebble_(watch)#Hardware

> The watch featured a 32-millimetre (1.26 in) 144 × 168 pixel black and white memory LCD using an ultra low-power "transflective LCD" manufactured by Sharp

Later generations are color, but it's the same tech. If you've ever used actual e-ink then it should be obvious enough that the Pebble displays are something else, it would be nowhere near responsive enough to keep up with pebbleOS's animations.