Final answer:
Color change in fish is caused by cells known as chromatophores, which contain pigments and reflect light to display different colors. In contrast, in humans, melanocytes produce melanin that protects the skin from UV damage and affects skin color.
Step-by-step explanation:
The color of both fish and human skin is influenced by pigmentation, which can include melanin. In fish, chromatophores are responsible for coloration and can change their size to alter the color and pattern of the fish's skin. These special cells contain pigments and reflect light at different wavelengths. In humans, melanin is produced by melanocytes, which are found in the stratum basale of the epidermis. The melanin is then transferred to keratinocytes, the skin cells that make up most of the epidermis, and helps protect the deeper layers of the skin by absorbing UV light.
We all have approximately the same number of melanocytes, but those in people with darker skin produce more melanin. This increased pigment production is a response to heredity and exposure to UV light, which also stimulates vitamin D production. However, because melanin blocks UV light from penetrating the skin, people with darker skin may be at greater risk of vitamin D deficiency.