The bones in the human body as well as that of all other vertebrates are made primarily from calcium, or to be more specific calcium phosphates. Have you noticed when you see an ad on television for osteoporosis, they often talk about whether or not a person (especially in women) is getting enough calcium. People with calcium rich diets have stronger bones and teeth because the calcium is food for those bones.
Now as to that generating the actual color white, calcium compounds usually refract the entire spectrum of light, just like everything else that is white.
Bones of the living body are not at all so dry, white and rigid, as we might think, seeing skeletons exposed in museums. Living bone is dark gray and is covered by a periosteum membrane, through which penetrate blood vessels and bones' nerves.
Although bones appear to be compact, in fact they are full of small cavities. Under the periosteum is following the compact tissue bone, Havers type.