A female rotkeil usually only has that bright red colouration when she is looking for a mate, paired or about to breed a single one would not have such vivid red colouration, its more of a hint of red. If my camera was working I could take a pic of my female rotkeil as she is now, a hint of red across the head, deep blue face with dark blue flanks, they are beautiful fish.
How do you feel about aequidens? there are so many nice once, the more common blue acara, the A. Metae (yellow acara) which I have kept with a large BGK and birchir before. Flier cichlids are nice.