@Little Guys that is too broad a statement. Some species will get best results over dark substrate while others do best over light substrate. For example, melanotaenia look best over dark substrate. If they live over light substrate, they wash out. However, neolamprologus multifasciatus look best over light substrate. When placed over dark substrate, they will begin to look more like neolamprologus similis. To the untrained eye that doesn’t know about the collar stripe, it most certainly would not be in its best dress. Cater to the species, simple.