From time to time, after bringing an image from ACR to PShop, I'll notice some really rough noise in a sky. My 5D has been pretty good at keeping that to a minimum. So, for a while, it was just a bogey. Tonight I finally found it, in ACR. If I ran up the luminance slider for yellow, grey clouds would start looking like Rodinal on steroids. So, not knowing really what that slider does, I'll use it more cautiously. What I was after, in so much ranch land scenery, was a way to control yellow so it was there but not so dominant; a way to lighten it the way you can in PShop in the saturation panel. Clearly Luminance must be a different animal. Didn't think it would be like patching out in a gravel parking lot!