Talk to Dermatologist on Black Spots On Skin

My brother is facing this issue he is having these dark black spots on skin , pic is attached below... black patches are occurring automatically there is no pain no swelling no itching nothing, just these black patches occur and if we look at them closely it looks like plain black patch inside the skin, these patches are occuring on legs and hip area , one thing i want to mention more my brothers wife is facing the exact same issue she is also having these patches which are blueish or black in color, is this some kind of allergy or what? Whom should we consult please guide is there any medicine for it