What is the name of the coloring matter that provides natural color to hair and skin?

Melanin is the term that describes the natural pigment found in hair, skin, and eyes, which gives them their color. This pigment is produced by specialized cells called melanocytes, and its presence and concentration determine the color of an individual's hair and skin. Higher levels of melanin result in darker shades, while lower levels yield lighter colors.

The other choices are not related to coloration. Keratin is a type of protein that is a key structural component of hair, skin, and nails, providing strength and resilience but not color. Cholesterol is a type of lipid found in cell membranes and is vital for bodily functions but does not influence pigmentation. Collagen is a protein that provides structure and elasticity to skin and connective tissues, again unrelated to color. Therefore, melanin is unequivocally the correct answer, as it is the active component responsible for the pigmentation in hair and skin.