The white one to me looks like a delta mismarked by Petco as a halfmoon. His tail/fins doesn't look halfmoony at all, but I haven't seen him flare yet at any of the other guys so I can't be 100% positive, cus my past boy Lyre looked like a delta, but when he flared you could tell 110% x infinity he was a HM.
I wish I could get him to flare so I could get a good pic. he sees the other guys and sits there next to the glass... my 2 new guys are so weird :P cus Knight, the melano I posted here seems anxious about my corys and took to them right away. I just placed their temp. containers next to eachother and he did 1/2 a flare (literally) and after that was content with them occasionally he will go up to them with his nose and check on them, and once he is satisfied they are ok will swim away (or so it seems like).