Zimmanski
Aquarium Advice Addict
I'm at the store now and looking at them and they all look female with pink bellys and Marley does look like he/she has the same shaped head more sloped as the females but not the pink belly like they do and not as much blue specks in the black dot Marley only appears to have blue flecks when in the light
My first thought was, "what freaking fish store is open at 11:40 at night?!" Then I saw where you're from haha.
Just grab the one that has the most female traits then try switching the tank around and hope for the best. Since marley seems to be the aggressor at least you don't have to worry about a new fish bullying a fish you're already attached to