A very good point, Chief Dan!
Looking again at the APoD, the dark part is dark, all over. The white part has many black spots, as if from incomplete coverage or later erosion of a white covering.
That giant crater near one pole (of the image, possibly not the real pole) has the rim on the side nearest to the dark side uncovered on the inner edge, as if by a glancing stream of white material. Other ridges and crater rims show a similar 'shadowing' effect.
Anyone who has spray painted an irregular object will have seen this effect.
White on black!
John