I honestly don't know for sure, but you may want to research Knight Goby. They are dull-colored, but truely a beautiful fish. On my most wanted if I ever go brackish.
You may also look into "Dragon fish"/"Dragon Goby"/"Prehistoric Goby". They can be territorial as they age, though, so I am not sure how they would interact.
I don't know if either of these would work with F8s, as I have heard mixed reports on their level of aggression, but these are fish certainly worth looking into.