For just a random opinion... We have had light tan sand in our larger cichlid tank for years, but recently started a new smaller tank with black gravel. I think the fish colors really pop more against the black gravel-but we also notice their orange poop really well too... The fish have always looked colorful against the tan sand, but theres not as sharp of a contrast as there is with the black. Ie- yellow on tan vs yellow on black. I'm curious too if anyone has an answer if natural habitat helps or not.