This started out as a little nub. Once it encrusted the plug it has shot up and out. The color actually looks a bit bore grey to my eye but this is the best pic I could get. need id by rworegon, on Flickr
It has tubular axial corallites and that's all we know for now. There are probably about 150-200 Acropora that will start off looking like that. So at the moment there is no way to even get close. Let it grow out untill it gets a defining shape and banches and bring it back.