Hi again, there`s really no such thing as a "Black" or "White" throat, that`s just the common name given in America, not widely recognised anywhere else in the world.
They are just sub-species of the White Throated monitor; V. albigularis albigularis, V. a. microstictus and V. a. angolensis. V. ionidesi is not currently recognised as a separate subspecies as far as I`m aware.