Ah, ok. Yeah, the finish is clearly chipping. My guess is some rough use, or maybe placing them flat against a desk over the years, resting on that part of the headband? My HD595's finish wore a little on the cups where I'd place them on the desk, but it took years. It didn't chip, but wore down to the underlying black material. The 6X0 series has a much glossier finish and it makes intuitive sense that it would chip rather than merely wearing away to the underlying material.
I keep my 650s in their box on my desk when I'm not using them, and after a year of daily use they still look brand new.