Chronic Venous Insufficiency: This condition is characterized by the inability of veins to return blood to the heart due to valve issues, leading to blood pooling in the legs. It often presents with dark discoloration (hemosiderin staining) of the skin, especially around the ankles, without a significant change in temperature.

Stasis Dermatitis: A condition that occurs due to fluid buildup in the legs, leading to skin inflammation and darkening. It's common in individuals with poor circulation or heart failure.
Diabetic Dermopathy: Also known as shin spots, this condition presents as dark, circular patches on the skin, typically on the shins. It's associated with diabetes mellitus.
Eczema (Stasis or Contact): Can cause darkening of the skin due to chronic inflammation and scratching.

Deep Vein Thrombosis (DVT): Although DVT typically presents with warmth, swelling, and pain, in some cases, it might not have these classic signs, making it crucial not to miss. The dark discoloration could be a late sign of a large clot.
Arterial Insufficiency: While this usually presents with pain, coldness, and pallor, in some cases, especially with chronic disease, the presentation might be atypical, including dark discoloration without significant temperature change.

Sickle Cell Disease: Can cause leg ulcers and dark discoloration due to sickling of red blood cells and subsequent tissue damage.
Sjögren's Syndrome: An autoimmune disorder that can cause skin discoloration among its myriad of symptoms.
Malignancy (e.g., Kaposi's Sarcoma): Rarely, dark skin lesions can be a sign of an underlying malignancy, especially in immunocompromised patients.