What causes the difference in pigmentation between people with darker skin and
people with lighter skin?

Melanin. “Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin color of darker-skinned humans. The skin color of people with light skin is determined mainly by the bluish-white connective tissue under the dermis and by the hemoglobin circulating in the veins of the dermis.” -Wikipedia

The high specific heat for the property of water allows it to remain unfrozen. There is also a very large surface area for the finger lakes.