Why is it colored in trees along the roads and highways?

So for I know there are two reasons one is to shield bark of tree from sun consumes serious virus impacts particularly during summer sunshine and night/night cold and to shield from rodants and different contaminations,

Somebody Anonymous, I am submissively noting your answer. Soil and smoke in the environment (from vehices, production lines, plants, petroleum processing plants) chooses the plant leaves and branches leaving them dirtier dark. Air contaminations, including sulfuric corrosive, blend in with water beads that structure mists.