If you want a whole lot of control on this and future epoxy projects, check into the coloring agents for epoxy sold through boat repair supply houses. I use them all the time for making epoxy bodies on flies. They come in about a dozen colors including brown, black, white and gray. You can blend to produce a perfect color match. For the small quantity of epoxy you'd use on this job, you probably need a bit of the coloring agent about the size of a pin head. A little of that stuff goes a long, long ways. Handy to have a selection of those little color tubes in a drawer any time you have to match colors for repairs.