Its hard to tell what it is at this stage. It could end up being similar to a garf bonsai. It's hard to tell. Typically, the polyp color on most acros like this doesn't change much and the polyps in this pic don't look very bright... but that could just be the pic. The skin color of course may get more purple. There are a lot of acros out there that look similar to the garf bonsai, there are at least 3 other LE corals I can think of with similar coloration and countless wild ones that have green polyps and purple base. I would definitely recommend getting it some more light for the time being and see how it responds. Knowing it came originally from Mark's tank means it could be anything... as he kept a very nice but eclectic collection of LE and wild corals. It definitely has potential though!