Hi dear there are points. First normally also the genital skin is dark and becomes more dark with age. But in ur case it is itching also. So it is a fungal infection
called as tinea cruris
. Dont worry much . Here is treatment for u.
Use oint clodid b once in night for one week. Following this use oint clotrimazole
twice daily for one month. Remember to continue for one month. U ll be fine. Thank u