When a dove begins to associate with crows its feathers remain white but its heart grows black?

This is saying that the nicest person can turn cruel within the crowd they are with. if say a smart girl who gets good grades goes and hangs out with slackers who don't care chances are she will start to act like that because they are influencing her to be bad. and they could pressure who too. you have to chose wisely of the people you hang out with or else everything can fall apart.