UPDATE: Nikon have had a look at the screen shots, the SOOC JPEG, maybe the Raw NEF in Capture NX-D and determined there is nothing wrong with my D810's. They say the the WB numbers in the manual are "approximate and not set values".
That seems odd to me since from the screen shots, the only anomaly is the Flash WB setting, the others are nearly exactly the same.
Anyway, note for those who shoot in JPEG only, don't expect the Flash WB to be what the manual says especially if you are shooting with non-Nikon flash units.