Hello dear, 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. Take care.