This is Tinea Versicolor also known as pityriasis Versicolor. It’s a fungal infection caused by a type of yeast infection called Malassezia.
If you have or you know someone who has this condition, show them this thread:
@GeorgeAnagli@KingsleyBangs You don’t know how helpful this has been, I’ve tried and tried so many things, brake fluid only cleared out the fungus on my arms, as for the back not even. The sun also plays a huge factor wow, makes so much sense now, no more shirtless beach days for some time now.