I don't know if this is your situation or not, but I have a friend who recently had the same "problem".
His new-to-him Ruger M77 showed strange light spots all along the length of the barrel. I noticed that they were spaced very regularly, and asked him how he stored the gun. He replied that he left it in a case, and pulled out a typical plastic hard-sided case lined with "waffle-type" foam. I lectured him a bit about the potential problems of storing any gun in a case, and then "solved" the "mystery" for him. The blue wasn't fading -- the high points of the foam were absorbing all the oil off of spots along the barrel, making what looked like a weird blue-faded condition. A light re-oiling and the spots were gone.