There are a number of fillers you can add to epoxy, resin or super glues to enhance gaps or splits.
There are spirit dyes, powder pigment colours and the brass, copper, silver and bronze powders that will give a metallic look when finished. There are also the "Inlace" products available over here that give the effect of tiny stones set in a coloured background, a bit pricey though. You could consider car body fillers, using spirit dyes with the normal one or buy the pure black colour.
When I add an epoxy filler I usually give it about 15 minutes to go off and then turn it flush with the surface, much longer than this and it becomes very hard to work.