It can be due to hyperpigmentation or melasma skin. Generally, this type of pigmentation resolves gradually and needs no attention. However, you can use cosmetic preparation that have demelanizing contents or seek a guidance of a dermatologist. Alternately, you have the option of cosmetic laser therapy to help you look better, though it may be a costlier.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.