If you are referring to subspecies, I believe there are only two subspecies Varanus acanthurus acanthurus and Varanus acanthurus insulanicus.
Varanus acanthurus insulanicus is basically found in the north east section of Arnhem land and nearby islands. It grows slightly bigger and is a darker form (some are very nice black and white colours). They are extremely rare in captivity, and photos can be hard to find. All up not much is known about them.
Varanus acanthurus acanthurus is basically the remainder of the range. It contains many different forms with the most common in captivity referred to as 'reds' and 'yellows'. These used to be separate subspecies but due to poorly defined descriptions and distribution were placed together. You could find 'reds' that were yellow and 'yellows' that were red. The 'Reds' used to be such localities as Pilbara, Sandfire, Kimberleys while the 'Yellows' used to be such localities as Mount Isa and Alice Springs.
There is a very similar species which is called Varanus baritji. These are almost the same as ackies and probably should be placed as a subspecies instead of a full species.
Cheers