Grayson I already thought of that, but here is the reasoning why black is the primary color... its dark and you can't "see" the bottom. With black I can get away with the bore being only about 3/4 - 1". With light gray I probably would have to make it more like 3-4" so you can't "see" the bottom. If the bore was 3-4" long and only about 1/4" in diameter, it would be an evil evil thing to put together. Otherwise I agree...
one last thought, if you wanted the deep bore look and still reverse the colors all you'd have to do is glue the rifling to the inside of the barrel before you roll it.