We were trying to duplicate the look of some older houses here in Atlanta where the brick had been painted and then sand blasted off. (This is a new house, btw). We used white mortar (and white sand) and had the brick masons "smear" a little mortar on the bricks with their trowel as they went. Of course we did a couple samples first to make sure we had the look we were going for. We also pressure washed the brick lightly at the end of the job.