system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the complexion of my penis (which gets no sunlight) darker than the rest of my body (which is constantly exposed to sunlight)?

Title.
gpt
Often the shaft will be darker and the tip will be lighter because the genitals generally produce more melanocytes to protect them from the sun, but the tip was generally hidden by the foreskin so it didn't have to evolve melanin.  This effect is exacerbated by the deflating of these parts in comparison to maximum volume increasing melanin density.  This was important historically to prevent dna damage to skin there.  It's not caused by blood, as stated in the other post as many pale people lack the melanin and color difference, but definitely do not lack the blood.