1. A vision system of a vehicle, said vision system comprising: a camera configured to be disposed at a vehicle so as to have a field of view exterior of the vehicle; wherein said camera comprises a pixelated imaging array having a plurality of photosensing elements; an image processor operable to process image data captured by said camera when said camera is disposed at the vehicle; wherein, with said camera disposed at the vehicle, said image processor is operable to process captured image data to determine a pattern of retroreflective reflectors present in the field of view of said camera; wherein said image processor compares a determined pattern of retroreflective reflectors to a database of patterns and classifies retroreflective reflectors at least in part responsive to determination that the determined pattern of retroreflective reflectors generally match a pattern of the database; and wherein the pattern of retroreflective reflectors comprises a first coding in gray shading and a second coding in color, and wherein a prioritized first set of data is encoded to the gray shading and a lower prioritized second set of data is encoded to the color.