The dark color of testicles is usually caused by melanin deposition. The skin color of human body depends on various pigments, especially the amount of melanin, the thickness of skin and the contraction or diastole state of blood vessels, and the important factor affecting the melanin deposition of skin is sex hormone. The concentration of sex hormones in the body’s sexual organs and other parts of the body is relatively high, and prolonged stimulation by sex hormones will lead to a large amount of melanin deposition, so the skin color will become darker, which is why the color of the reproductive organs of boys is usually closer to the color of the body’s skin, and the color of the sexual organs will gradually become darker when they enter puberty and start to develop. From the above, we can see that the darker testicles are a normal physiological phenomenon, caused by the stimulation of sex hormones leading to a large amount of melanin deposition, so patients do not need to worry too much and do not need special treatment.