Please post the clinical picture of the affected area for a more rational diagnosis from our side. 6 months is too less a time to expect reversibility of the changes caused by tobacco habit which must be a few years old at least. Going roughly by the description that you have mentioned, all I can say is that white patches with burning sensation are signs which warrant proper clinical evaluation. The black colour can be due to melanosis of the area and this can happen during the healing phase also although that is not always the case. So the best option will be to consult an oral pathologist so that the right diagnosis can be made and the right treatment can be instituted accordingly. Regards.