What Causes Dark Skin After Mole Removal?

Hi, I had 3 moles removed 4 months ago and they were cauterized with silver nitrate. Now 4 months later, one of the scars on my shoulder has a white center (wich is scar tissue) and is surrounded with darker skin(brownish color). Will this brown coloration around the white spot (normal)eventually fade back to normal skin color or is it permanent? How long could it take? The other two mole removals have a dark pink color (like a wound when your scab falls off ). I suppose these will fade. How long also?