@PoP: Just to double-check: did it ever work as you wanted it with earlier versions?
EDIT: Okay, tried it, no, don't think that's doable, that's an artifact of how eInk handles the update. I'll see if I can fiddle with different waveform modes

.
EDITē: Yep, it's a byproduct of GC/GL waveform update modes

. And those that don't work like that do not support so 'many' colors

.