Were mulatto slaves treated differently from the regular black slaves?

Sometimes yes. See the following.

YouTube.com/watch?v=UpT1fz1sElg&eurl=">http://www.YouTube.com/watch?v=UpT1fz1sElg&eurl=http://www.websitetoolbox.com/tool/post/mulattodebate/vpost?id=3254640&feature=player_embedded