Peppered moths weren't always dark, and they always didn't have those dark "peppered" spots on their body. According to the project we did in science, many people in England thought of different reasons to why the peppered moths had different body color. The main reasons is because the darkness in the moth is a genetic thing. The moth's offspring will usually have that gene, which is why there are dark spots on the moth. The other reason is from natural selection. Scientists thought the color change of the moths was an example of natural selection. Natural selection explains how species evolve and change over time.
In this case, the moths changed because of pollution. Their natural habitats were being polluted by factories, so they learned to adapt and change to that. The pollution of gas caused the forests to become dark. I think the color of peppered moth will stay the same. It helps them survive in the wild, and nothing has been changed.