Answer:
Well I'm not smart either. But i'll give you the answer.
Step-by-step explanation:
Since the population of gray squirrels and brown squirrels decreased, and the population of black squirrels increased, that means the gray and brown squirrels were eaten/left and didn't blend in very well to their habitat. However, the population of black squirrels increased, so they blended in well with their environment. This tells us that the color of the trees became darker, closer to black, since there were more of them.