The
correct spelling is 'Wight' rather than 'White', but why this word with its
unique spelling was adopted after the Romans left is not entirely agreed on
by the experts. All do agree that it was nothing to do with the colour of the
white cliffs. The most popular theory seems to be that the original meaning
of the word 'wight' was to 'split or divide' and related to the Island dividing
the waters off Portsmouth and Southampton.
The only thing that can be said with any degree of certainty is that the Island is not spelled Isle of White!
During the occupation by the Roman Empire 50 to 400AD the Island was called 'Vectis' and the word Vectis is still much in use on the Isle of Wight today. But the name was dropped when the Romans left in the 5th Century AD.
More information about the history of the Isle of Wight