Only a few black dots to turn the other way ...
Right now everything on the eink side is white to start with.
You turn around characters to the dark side to show characters and when you refresh you turn the dark sided characters to white and then turn the fresh characters to the dark side.

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In the illustration above shows a reverse layout. Everything is turned to the dark side initially and the refresh only turns the white characters to dark and proceeds with turning the new characters to white !!!

Refresh should take the same time. All this is provided eink low level interface is dark side neutral !