Peppered moths vary in color from light gray to almost black. The color of any moth depends on how many black spots are found on its wings. The name "peppered" refers to these black spots. During the day, the moths rest on trees. In England where the moths live, many light gray trees were covered with soot that came from the smoke stacks of factories. The trees got darker and darker from the soot. Over time, the moth coloration became darker.