I think the spear and scroll is a bit elaborate for a cutie mark. It could work, but they'd have a lot of trouble going unnoticed. Why a spear and scroll specifically? What colors are they? Why? Just little things to ask yourself, especially as a writer to really flesh out White Belt~ <3
I think white coat/black mane is always a safe bet. If you are really feeling a color change what about adding shades of grey into his mane? I live for tri color manes, and I bet a monochromatic coat/mane would look pretty sick!