merfolk can camouflage to hide from predators. as they adapted to human fairing the ocean, they learned to look more human like an use their camouflage to change into a more vibrant friendly appearance! because humans are dumb and easily frightened by stuff that makes us uneasy, they are less likely to die like this... Scott just uses it for evil

I reaaaally wanted to play with bioluminescent Mer!Scott some so this is an Experiment