I had a cut on my thumb but it grew back as big white scab instead of the usual dark brown scab. everytime i remove it the same white scab grows back.

A couple of thoughts: The usual cause of white scab is moisture within the scab usually caused by bathing/showering. Also, if you have put a lot of ointment or cream on a scab, that contributes to moistness and a whiter color. Finally an infection can be present with accompanying pus cells or even a virus producing a wart. I would be most suspicious of this. Consider seeing a Dermatologist for diagnosis. Good wishes:)