I have had this happen to myself last summer. I had shellac French on my nails and after a few days at the beach my shellac had a yellow/orange hue. Once winter came this went away, so I assumed it was because I'm at the beach 4 days a week. my clients never experienced until last week. I had a client come in and she was wearing a light pink color, however, the shellac was yellowed over the area of the nail beds and still the pink over her free edge. She said she hasn't done anything out of her normal routine and she is not a tanner. We both had this over our natural nails and our natural nails were not yellow after shellac was removed. Any clue why this may be?