Look into Tinea Versicolor, caused likely by a fungal/yeast organism, Malassezia furfur or other Malassezia species.
This is what I had a few years ago on various parts of my body,
face, chest, arm and legs, but only lasted for a a couple weeks.
I shampooed daily with Selsun Blue, applied an antifungal cream,
consumed 6 tablespoons of coconut oil daily ( my normal is 3T)
stayed out of the sun and lowered my stress levels by doing meditation twice a day. This regimen worked for me.
There probably other possibilities you can explore, but if your symptoms persist or worsen, you may need to visit a dermatologist.