Nice!
Not only is it a GG, but its a red tail GG
I saw your other thread about the pricing for a GG, and I had a strong feeling that this fish was in housed in a tank much too small for it. I'm betting the original owner just wanted to get rid of this behemoth, and probably would have given it away for free, but figured what the heck and just put a price tag on it.
Anyways, I think now that he's in an appropriate sized tank, with good husbandry those colors and that tail will come back nicely. My platinum GG is about 15" now and is very personable, but doesn't care for tank mates. I give him plenty of fruits and veggies daily, and pellets a few times week.
Wow I had no idea that he was a red tail! I just figured that he was a normal grey GG. Either way I love both color patterns!