I have made four colour maps now in B-V on four different nights.
The nights are arranged like this:
A uniform scale is used for all four images, from B-V = 0.0 to 1.4. The BS light is coming out in all four images around B-V=1.0, and the ES at around B-V = 0.6-0.8,
depending on whether one is looking at highlands or lowlands (lowlands are redder).
The cause of the black dips along the BS rim is the problem that the B images are slightly larger than the V images – so even with good registration of the center of the moon (to the closet pixel), there are issues in producing these colour maps. The falloff in the halo light cannot be the same power law in V and B, because the halo changes colour — but this is still to be checked.