As the investigations have ruled out the possibility of venous insufficiency
, the dark spots can be attributed to hyper-pigmentation of skin secondary to hormonal imbalance, systemic causes like diabetes
, or due to primary dermatological causes.
Investigations like complete blood count
, estimation of bleeding & clotting time, blood sugar level & blood pressure & Thyroid profile will be helpful to rule out any pathological cause for the symptoms.
So, kindly consult your General Physician/Dermatologist
& get a proper clinical examination done.