Units comprised of red, green, and blue L.E.D. clusters, would replace normal red brake lights, white reverse light(s), and/or orange turn signals.
These would have an infinite range of hues, allowing for much more accurate signaling.
For example, it could be programmed so that light pink would
indicate slight braking; bright red would indicate maximum braking, and everything in between. Rapidly alternating orange and pink for example could indicate turning. Green could mean there is a safe distance for the car behind you to accelerate, or it could display red if it is not a safe distance, and it could be automatically controlled using radar (Radio Detection and Ranging). Reversing could be signaled by all three colors (RGB) being on at once, creating white light.
It could have white translucent plastic covering the LEDs, to blur the light.
Smaller versions of it could be placed on the front of the vehicle.
It could also possibly be programmed to show different shapes like an arrow for turning etc. And it could display different colors in different portions simultaneously.
It could even be programed to show very low resolution animations.