I've had this problem with my camera since day 1. Nikon have had the camera in for a service, check up and up date and says that all is well. I would be interested to hear if the problem is universal. I would also be grateful for photoshop correction advice, in easy stages if possible. I have had help on this subject a year or so ago but thought a revisit would help. In very clear weather the camera records obvious banding in the sky. I don't know if its because of clipping in the blues or an inability for the sensor to cope with extreme levels of blue. It records the same on jpegs and raws, so has little to do with compression, and shows on prints big time. Day time or evening shoots don't make much difference only the clarity and saturation levels of blue seem to be the main influence.