There are a few Cichlasoma that are pretty drab. Some have black edged scales. Some have pretty iridescent scales like dimerus. They are difficult to ID but the body shape and fin pattern are definitely Cichlasoma.
At first glance I'd say an Acara. Only seen them in stores, so I can't tell you which type of Acara if there are other species. But it is hard to see with the lighting of the picture :/