Wall color is really off. I did a mortar wash on my brick - much less than a German schmear. In your case you simply take mortar mix, a couple of drops of grey paint that matches your floor into the mix. You make the mix really runny, paint it on and as it drying, you then wipe it off. It will make the brick look old without overpowering it. I think the German schmear is just too much. Don't paint brick on a fireplace it makes a mess of the brick.
Q