Thanks Alex, should I add some tank mates for him/her and if so what would be recommended? Ive had this one for a couple months with no other anthias and it hasnt changed colors at all.
It's not a Pink Square. I would say rubrizonatus or marcia. It should stay in the 5" range but someone said they had seen some in a public aquarium at 8". My male is at 4" right now and he has grown a little. The fish in the picture you posted is definitly a male. Here are the two males I started with (one died for no reason, two weeks in), and my female for reference. I'm not sure the female is the same species, but she looks close enough and the male treats her like a female of the species.
As for his care, I would definitly recommend finding a female. Mine has done fine with just the one, no aggression whatsoever towards her. If you do try to find one, I highly recommend not buying without seeing the fish first. They are extremely difficult to correctly ID and usually only the males are collected. I found my female when an LFS got in a "potluck" group of anthias that had a few in there. I had just the male for awhile and he dramatically colored up when I added the female.
My male is definitly the king of the tank, but it's a very peaceful tank and he's not really aggressive towards anyone. I could be lucky, but he's just getting started out in a 125, so the experiences I'm sharing are from his few months in a 65.