getting brown flat spots on my skin after it heals

Hi, welcome to the ehealth forum and I am glad to help you.
You seem concerned by the flat brown spots after injury which is called as postinflammatory hyperpigmentation in medical terminology.
The discoloration can last for weeks, months, or even years and turn into a permanent scar. This type of hyperpigmentation can occur with any skin type but is especially common among people whose skin has more color — not just dark skin but light brown and olive skin as well. Sunscreen can help prevent postinflammatory hyperpigmentation and keep the area from darkening further. If the discoloration really bothers you, you must consult your dermatologist about using a skin lightener, chemical peel, or microdermabrasion to treat the darkened spot.
Hope this helps. Take care.
Note: This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.