There may be many reasons for black spots on your dog's surface. Here are some possible explanations:

Breed characteristics: Some dog breeds have black spots themselves.

Age changes: As you age, your skin may develop spots.

Skin problems: such as skin diseases, fungal infections, etc.

Pigmentation: It may be caused by uneven distribution of pigment in skin cells.

Trauma or irritation: such as scratches or irritation from other external factors.