Limestone Stair Treads

We had masons completely remove our old steps to the main entrance of our Northeastern NJ home and (http://maplered.com) install new steps. They are filled with concrete. The sides and (http://maplered.com) front are brick. The step treads are limeStone (http://g603.net) and (http://maplered.com) the top edges are limeStone (http://g603.net) with blue Stone (http://g603.net) laid in the center.

The limeStone (http://g603.net) was white before installed and (http://maplered.com) then had a brownish color after installed as if it absorbed the concrete. The installer said at the end of the process, when the concrete had completely dried, they would acid wash them and (http://maplered.com) they would be nice and (http://maplered.com) white again. It took 10 months and (http://maplered.com) a lot of phone calls ( a separate issue) for them to come back and (http://maplered.com) apply this "acid wash" and (http://maplered.com) the steps still look discolored with some spots of white powdery stuff.

Is this acid wash a real process? If so, was it too late to do it? Are my steps permanently discolored? If not, how can I make the limeStone (http://g603.net) white?

Thank You