When a yellow Bakelite is heated it darkens from yellow to red to dark red to black. Some Bakelite formulations were unstable at room temperature and turned from yellow to red without extra heating. The surface of a Bakelite bead also gradually browns with age from exposure to air and light. The color changes in both cases are typically in a very thin layer, so if you start polishing or grinding the surface, you may change the color of that spot quite a bit, and then it won't match the rest of the bead. I have experimented with a number of Bakelite beads, including cutting them in half to see how deep the surface color extends - and it's only fractions of a millimeter in most cases.
The other possible outcome when a Bakelite bead is heated is that the color change in that spot could go much deeper, making it impossible to polish or grind off.
My recommendation is to enjoy the bead as it is and not remove any of the age or burn-related color change. It's part of the uniqueness of Bakelite beads. If you want a plastic bead of uniform color there are a lot of them out there, usually made from polyester resin. And of course there are a lot of Bakelite beads for sale that have not been burned.
