The answer to this totally depends on _how long, since when, _and _to what extent _has the person been blind.

If a person has been blind since birth, they’d just have auditory dreams, i.e. all dark, with just voices. but if a person used to be able to see, but lost his sight later, they’d dream just like normal  people do i.e. in color, _or perhaps, as they get used to being blind, their dreams might reduce to auditory ones, and if they arent completely blind, but cannot exactly dream very well either, and _have been this way for a long time,  their dreams too would be all blurry and obscure, just like their vision.

I never exactly met a blind person to ask, but well, after researching a bit, and well, applying a bit of common-sense, stated above is what i believe.