Just found a diagram - the area I think you are referring to is according to some diagrams occupied by some of the attitude control thrusters ..it’s mostly recessed, irregular in profile, and covered in a thermal blanket of some sort so it’s not a rigid panel, and there are a few nozzles sticking out through the blanket…, there certainly appears to be some discoloration, perhaps due to thermal effects or chemical effects but no idea if it was expected - wouldn’t be completely surprised if it was normal.
There still some debate going on about the attitude excursions that went on post docking……………