Yeah when my sorority wasn't as heavily planted none of my females showed very vivid colouring and the less dominant ones hung out at the back and bottom refusing to come up for food.
If your tank is rarely sparsely decorated you will sometimes see no aggression as the females feel to exposed and stressed to fight.
If you don't do live plants, I'd fill it up with fake plants. Those imitating stem plants and plants such as swords and vallisneria are ideal as they will offer cover at all levels of the tank. I'd use some PVC pipe in T and L shapes on the ground as your females can swim in and out of these without getting trapped, which is what can happen in terracotta pots.
This is what a healthy sorority looks like. All of my females are bright, healthy and while there is still the odd nip or two, no serious fighting or chasing occurs. Please note I have since added more plants since this photo as I was waiting on a delivery.