It's common for the penis and testicles to be darker than the rest of the body, and if some of your ancestors were perhaps quite dark-skinned, then it wouldn't be surprising if this made your genitals rather darker.
The changes in the colour of skin of genitalia from puberty onward is just normal. The groin area pigmentation may follow tinea cruris, friction of undergarments and above 40s due to acanthosis nigricans. Acanthosis nigricans may have association with obesity, or endocrine disorders like diabetes mellitus, rarely due to underlying malignancy.
It is true that fungi such as Pityrosporon can darken the skin. However, it wouldn't make any sense to treat yourself with an anti-fungal medication when no proper diagnosis has been made.
The obvious thing to do now is to ask your GP to look at your penis and testicles, and to decide whether you really do have a fungal infection.
It would be advisable to consult a skin specialist for your symptoms and a proper clinical examination.
Let us know if you need any other information and post us on how you are doing.
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