They may respond to any type of stimulation. This is called referred pain. Merkel's discs are touch receptors. They are most numerous in the fingertips, palms, tip of tongue, lips, nipples, clitoris and tip of penis. The End Organs of Ruffini detect heavy and continuous touch sensations.
Skin color depends on several pigments.
This is an epidermal pigment. The amount of melanin yields colors between pale yellow and black. Melanocytes are derived from melanoblasts. Maximal numbers of melanocytes are found in mucous membranes, the penis, nipples and areola, labia, face and extremities. The number of melanocytes is about the same in ALL races.