I don't know about Biewer's but I have had a couple of dogs change color on me as they matured. When we got our Shih Tzu he was a tri-colored puppy. By the time he was an adult he was mostly white with some gold and all the black had disappeared. Gracie had the typical black Yorkie saddle on her as a puppy and her black lighted up quite a bit as she matured. I guess they decide for themselves what color they want to be!
