My largest Male Amarillo is about 4 to 5 inches and is trying to mate with my female devil. I know she is female because she had fry from another devil. My Amarillo has a large nuctal hump already. He loves to fight my larger Umbies but as you can see he gets shredded up, lol, but that doesn't deter him. I don't know if all males get the head hump? I think he is in breeding dress in the pic's. Has some red going on in the head.
Maybe both of yours are females? or wait till they pair up and then you will easily be able to tell.
Nice fish you have there!! I love the personality of these guys.