Braun (brown) is very common among non-Jews, so is Roth (red, in modern German: rot), Schwarz (black) and Weiß (white). Grün (green) is most likely Jewish. I am sorry, I can't explain why. Um..back around the 17th and 18th centuries(it may have been earlier) alot of Jews were made to adopt surnames and many of them chose names that had to do with colors, gems and precious metals. They would also adopt generic sounding European names too, to blend in better, and they would commonly adopt the name of the town they lived in as well. For instance, Steven Spielberg, Spielberg was the name of the town his family lived in at the time they adopted that surname. But alot of regular Germans also used the name of their hometown as a surname, for instance, the farming family I grew up by who are undeniably German, and their name is Bamberg, which is the town their family originated from in Germany. So it can be very difficult to tell a Jew just by their last name sometimes.