They undergone genetic mutation that influenced their fur color.
Mutations result either from accidents during the normal chemical transactions of DNA, often during replication, or from exposure to high-energy electromagnetic radiation (e.g., ultraviolet light or X-rays) or particle radiation or to highly reactive chemicals in the environment. Mutation can be of 4 types Germline mutations occur in gametes. Somatic mutations occur in other body cells. Chromosomal alterations are mutations that change chromosome structure. Point mutations change a single nucleotide. Frameshift mutations are additions or deletions of nucleotides that cause a shift in the reading frame. Factor that influenced mutation are the size of the gene, its base composition, its position in the genome, and whether or not it is being actively transcribed influence its mutation rate.
