We are thinking of purchasing an RT and am wondering if the colorings of the breed changes as they get older? We are looking at a 4 month old male with a black & brown face and white body. What is the possibility of that changing? Thank you in advance.

What you are seeing in terms of coloring at this point is what you get with the exception of ticking.  Ticking is black spots on the dogs skin.  Those become more pronounced in the summer and appear less visible in the winter.  When the dog gets older he/she will go gray in the face (just as humans get gray hair, so do ratties).