The Idea
A creature evolved or engineered to communicate exclusively through color. The RGB bioluminescent bulb is its only voice; the ocular system is its only ear. Every word is a flicker. Every sentence is a fade. To anyone without eyes. Humans included, in the dark. They are perfectly silent.
The Survival Logic
Two opposite environments would favor it. Somewhere too loud for sound to mean anything (a factory, a waterfall, a hurricane belt). Sound communication is wasted. Somewhere too quiet but full of predators with ears (a forest at night). Sound communication is fatal. Light, in either case, is the better channel.
What It Echoes
Cephalopods already do this with chromatophores. Deep-sea fish already do this with bioluminescence. The Light-Communicators are what happens when that biological grammar gets formalized into a robotic species.
Status
Concept.