I did the same to some stag handles on a folder, many years ago. Edges were pretty 'square', like in your pic. I'd assume at least some of the color would be removed, on the dyed bone. I don't have any experience in re-coloring bone scales, so hopefully you'll get advice from others here about that.
If I were going to undertake this project, I'd begin very gently, with fine-grit sandpaper (around 1000 grit or so, give or take). Sounds like you're not planning on removing a lot of material from the edge, so I think the fine grit sandpaper should do the trick, without being too aggressive or leaving heavy scratches afterwards. I've found a small, flexible art/drafting-type eraser (I use a 'MAGIC RUB' eraser) to be very useful as a sanding 'block', around which I wrap the sandpaper. The flexibility of the rubber eraser will make it conform naturally to the contours, without 'flat-spotting' them. I'd also recommend some dust protection for your nose/sinuses/lungs. I've heard the dust from sanding bone/stag and other materials can be toxic, if inhaled.
Good luck.