Unless you know it came from G.A.R.F. then it can't be Bonsai. There are monay Acropora species that can be Purple with green polyps. They are not all Bonsai Acros. Only the frags that come from the original GARF colony are. Bonsai does not have white tips either. It looks more like an Acropora valida to me. Acropora valida. Corals of the World - Photos, maps and information about corals and reefs