Congratulations on your two boys. Many people call the Biewers "Rainbow dogs" as they can change colors and some do so many times. Most of the color changes are usually on the head. The black can break to the blue and yes, sometimes the gold and white can change as well. On the body, most of the color changing occurs on the back. While most tend to keep the black, some do break to blue. You will also see dogs break color (usually blue) where the white is.
Personally, I have not seen where a black tail breaks to have a white tip nor have I seen tan legs change to white. These dogs never cease to amaze me, so I wouldn't say that it can't happen....just highly unlikely that he will end up conforming to the standard when it comes to coloring.
Can't wait to see the pictures and congratulations again!
__________________  Jen and the Bloomin' Biewers Gang |