The display driver includes a command to invert the display and I have included a facility to choose an inverted display in the Settings app. I am still undecided as to which setting is more readable, however after implementing the analog clock app shown below, I noticed some ghosting of the second hand with black on a white background which is not visible in the inverted display.

I had thought that having the clock display update every second might reduce battery life, however so far this has not been noticeable. The time to update the display for the second hand is 40ms so this represents only a 4% increase in CPU usage which is the only increase in power consumption. Unlike E-paper displays which take a lot of power to update but none when quiescent, the power used by these reflective displays is more or less constant.