What causes hyper pigmentation under the eyes?

58 year old female of Indian origin, an immigrant in the US for over 30 years, compalining of hyper pigmentaion under both eyes on her face for few years. Had dermatology and rheumatology consults wth no major findings. Chemical peeling helped with local steroid application but response only short lived. A rheumatologist thought she may have FMS as she wakes up with burning pain on her ers and both arms only when she lays down to sleep. In fairly good physical health except for taking synthroid 50 mcg a day. Now presents with raised macular rash on both sides of her face next to her nose as if like in a butterfly distribution without pain or itching. She was out yesetrday in the sun in a waterfalls area which was mostly a shaded area. She took Benadryl 50 mg last night and applied steroid creme and took naproxen today am and the macular rash disappeared, but still the bilateral hyperpigementation under her eyes on the face which exacerbated is still there. What are the diagnostic possibilities? She was checked out for SLE a few years back which was negative then.