DS's are still changing.
They will probably go completely brown but at the moment there are still flecks of blue so its official blue/brown hazel.

Our "chances" are.. 50% brown, 37.5% blue 12.5% green

Also with hair colour there are multiple genes involved and it is harder to predict. Red hair can pop up when it hasnt been in either family for generations.

DHs hair was blond til he was 8 and then it gradually got darker, its quite a dark brown now.