I've had a purple tip green polyps Acropora (species I really don't know) for many years that I got in a trade with the guy running the coral tank at the New England Aquarium. That was probably >15 years ago. I call mine the NEAq Purple with green polyps Acropora. Back then we did not do a lot of fancy naming. Are you specifically looking for a species name, because those are very difficult to get with Acropora genus.