Answer:
Scattered groups of melanocytes in the skin causes the skin to appear darker in groups with more functioning melanocytes and the skin to appear lighter in groups with less/no functioning melanocytes.
Step-by-step explanation:
Melanocytes produce melanin, which is a dark pigment. Thus, if the skin has fewer melanocytes, less melanin is created in that area, so a smaller amount of dark pigment is present, resulting in a lighter color. Likewise, if the skin has more melanocytes, more melanin is produced in that area, so a larger amount of dark pigment is present, resulting in a darker color.