Good question! Everyone's skin is different, and for many people, the skin in the area of or around your genitals may be darker (scientifically called hyperpigmentation). This may be due to hormones like estrogen, which can impact our skin color sometimes by stimulating our melanocytes (cells that make the pigment or color on our skin), or friction on your skin, which causes the color to get darker over time.
As long as there is no irritation, reddening, or a sudden darkening to a color you haven't seen before, darker skin in the genital area is normal. If you are ever concerned, you can always ask your doctor about it as well.