A reflector unit may behave as a retroreflector to reflect light of a selected color. The reflector unit may comprise a first reflector having a first color, a second reflector having a second color, and a mask that either allows incoming light to reach the first reflector and not the second reflector or allows incoming light to reach the second reflector and not the first reflector. An active light unit may emit light of a particular color in response to receiving light. In this fashion, the active light unit may simulate the operation of a reflector. The reflector unit and the active light unit may operate on a bi-directional vehicle.