Patina forms because it has a place to start, meaning that parts of your blade are not polished adequately and give the corrosion a place to begin forming. I never see any on mine, but not only do I carefully dry them, I buff them in a stropping motion on a doubled towel to bring back the shine and remove any residue. The residue, however slight, is a place where water can interact with the blade and start corrosion, seen first as patina. If that doesn't work, I would polish the blade using Flitz, Maas or a polishing compound of some sort.