What skin disease is this?

Here's why:

• The patches have irregular shapes and borders, which is typical of something applied externally rather than a dermatological condition originating within the skin.
• The skin texture within the dark areas does not show signs of inflammation, scaling, blistering, or significant textural changes that are commonly associated with most skin diseases.
• The underlying skin appears to be of normal color and texture where the dark patches are absent.

Therefore, this appearance does not strongly suggest a specific skin disease. For any persistent or concerning skin changes, it is always best to consult a healthcare professional for a proper examination and diagnosis.