"Below" in this context means "directly below and connected by a line" (the lines are the edges of the cube). So you can have a blue vertex that is vertically below a white vertex, so long as they are not connected by an edge. The first time this can happen is for a 3 dimensional cube. You can have blue at the top, then 2 blue and 1 white below that, and then 1 blue (under and between the 2 blues in the layer above) and 2 white in the layer below that, and then white for the bottom vertex. This configuration can be rotated 3 ways and this takes us from 17 to 20.
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