as i mentioned previously, it's not that all unusual. you are looking at light corrosion buildup on the zinc plated outer shell of the bearing outer race lip. bikes do this all the time. no indication at all that bearings are failing. you will know it if and when your wheel bearings go bad. you can feel and hear it when simply moving bike around in your garage. or jack up each end, spin wheel and grab at 6 and 12 o'clock and wiggle wheel assembly. if you feel slop in the wheel when doing this or hear something any noise in the hub area, then the bearings are failing. if you don't pressure wash your bike the bearings should last a long time.