Most street legal vehicles utilize a combination of three colored lights: white for headlights and reverse lights, red for tail and brake lights, and orange for blinkers....
Mercedes-Benz debuts turquoise exterior lights to indicate the car is self-driving | A visual indicator for other drivers::undefined
If only there was some kind of universal communication technology that didn't require line of sight, worked over distances out to say 100m and was reasonably inexpensive to implement...then we wouldn't need to communicate using the modern equivalent of semaphore.