Question

The change of a common color from light to dark in the peppered moth is what

Answer 1

Well while the peppered moth is mainly light colored, it is noted that from time to time a dark individual is to be found purely as a result of random variation.
The important thing to appreciate is that in the English midlands where pollution had made all the tree bark dark, these dark individuals survived and bread because birds could not see them against the dark bark. Thus over time the peppered moth population in the English midlands was made mainly of dark colored individuals.

Answer 2

The force that causes this random variation is natural selection.

Answer 3

@One098