I'll bet you are talking about KPK's. The standard nut and saddle used to be ebony. I have an acacia concert with ebony, and it has a lovely "Kamaka-like" woody tone. A bone nut usually makes an instrument sound brighter. Ebony is harder than the standard rosewood they now use, but I'm not sure by much. I think the KPK's are bright enough without the bone, but that's a matter of personal preference....a slightly woodier mellow tone vs a brighter one. It's your call.
http://theunofficialmartinguitarfor...y-vs-Bone-vs-Ebony-NutSaddlePins#.Uvl6w-mPI5s
An interesting discussion on the matter: