Hello, You may have a viral ulcer since you report this location with a prior occurrence. The changes with inflamed tissue may appear very dark. Trauma to an area with dried blood or hematoma may appear dark in color. Different pigmentations in tissue can be normal such as a nevi or a change of tissue color can indicate concern requiring a biopsy to evaluate for a melanoma. An amalgam tattoo can occur with removal of older filings. I suggest rinsing the area with warm salt water. Maintain a soft diet, gentle daily dental care, stay hydrated and avoid acidic or spicy foods. Continue to monitor the area noting size, shape, texture and discomfort. A clinical diagnosis by your dentist will put your mind at ease. Your dentist would determine if a biopsy is needed to determine pathology of a suspicious lesion. As long as the area is healing and not showing abrupt changes, there is most likely less need for concern. Make sure you discuss your concern with dentist at your next dental visit. Thank you for your inquiry. I hope you find my comments helpful.